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Tutorial
PartiQL provides an interactive shell that allows users to write and evaluate PartiQL queries.
PartiQL requires the Java Runtime (JVM) to be installed on your machine. You can obtain the latest version of the Java Runtime from either
Follow the instructions on how to set
JAVA_HOME to the path where your Java Runtime is installed.
Each release of PartiQL comes with an archive that contains the PartiQL CLI as a zip file.
-
Download.
You may have to click on
Assetsto see the zip and tgz archives. the latestpartiql-clizip archive to your machine. - Expand (unzip) the archive on your machine. Expanding the archive yields the following folder structure:
The file will append PartiQL's release version to the archive, i.e., partiql-cli-0.1.0.zip.
├── partiql-cli
├── bin
│ ├── partiql
│ └── partiql.bat
├── lib
│ └── ...
├── README.md
└── Tutorial
├── code
│ └── ...
├── tutorial.html
└── tutorial.pdf
where ... represents elided files/directories.
The root folder partiql-cli contains a README.md file and 3 subfolders
- The folder
bincontains startup scriptspartiqlfor macOS and Unix systems andpartiql.batfor Windows systems. Execute these files to start the REPL. - The folder
libcontains all the necessary Java libraries needed to run PartiQL. - The folder
Tutorialcontains the tutorial inpdfandhtmlform. The subfoldercodecontains 3 types of files:- Data files with the extension
.env. These files contains PartiQL data that we can query. - PartiQL query files with the extension
.sql. These files contain the PartiQL queries used in the tutorial. - Sample query output files with the extension
.output. These files contain sample output from running the tutorial queries on the appropriate data. - Alternatively, you can use the online CLI Tutorial.
- Data files with the extension
Run (double click on) partiql.bat. This should open a command-line
prompt and start the PartiQL Shell which displays:
Welcome to the PartiQL shell!- Open a terminal and navigate to the
partiql-clifolder. - Start the REPL by typing
./bin/partiqland pressing ENTER, which displays:
The folder name will have the PartiQL version as a suffix, i.e., partiql-cli-0.1.0.
Welcome to the PartiQL shell!To get a deeper understanding of PartiQL, check out the CLI Tutorial.
PartiQL provides SQL-compatible unified query access across multiple data stores containing structured, semi-structured and nested data. PartiQL separates the syntax and semantics of a query from the underlying data source and data format. It enables users to interact with data with or without regular schema.
The implementation currently only supports data without schema. Schema support is forthcoming.
This tutorial aims to teach SQL users the PartiQL extensions to SQL. The tutorial is primarily driven by "how to" examples.
For the reader who is interested in the full detail and formal specification of PartiQL, we recommend the 2-tiered PartiQL formal specification: The formal specification first describes the PartiQL core, which is a short and concise functional programming language. Then the specification layers SQL compatibility through syntactic sugar that shows how SQL features can be translated to semantically equivalent core PartiQL expressions. These translations presented as syntactic sugar enable SQL compatibility.
PartiQL is backwards compatible with SQL-92. We will see what compatibility means when it is used to query data found in data formats and data stores.
For starters, given the table hr.employees
Id name title
-------------- ------------- ----------------
3 Bob Smith null
4 Susan Smith Dev Mgr
6 Jane Smith Software Eng 2
the following SQL query
SELECT e.id,
e.name AS employeeName,
e.title AS title
FROM hr.employees e
WHERE e.title = 'Dev Mgr'
is also a valid PartiQL query. As we know from SQL, when this query
operates on the table hr.employees it will return the result
Id employeeName title
---- -------------- ---------
4 Susan Smith Dev Mgr
INFO
For convenience we have provided the file
tutorial-all-data.envin the folderTutorial/code/. You will also find separate.envfiles in the same folder for each query in the tutorial.For example, running
./bin/partiql -e .wiki/assets/code/tutorial-all-data.envwill load all the data used in the tutorial in the REPL. This will allow you to copy-paste queries from the tutorial into the REPL and try them out.
PartiQL operate not just on SQL tables but also on data that may have nesting, union types, different attributes across different tuples, and many other features that we often find in today's nested and/or semi-structured formats, like JSON, Ion, Parquet, etc.
To capture this generality, PartiQL is based on a logical type system: the PartiQL data model. Each PartiQL implementation maps data formats, like JSON, Parquet etc., into a PartiQL data set that follows the PartiQL data model. PartiQL queries work on the PartiQL data set abstraction.
For example, the table hr.employees is denoted in the PartiQL data
model as this dataset
{
'hr': {
'employees': <<
-- a tuple is denoted by { ... } in the PartiQL data model
{ 'id': 3, 'name': 'Bob Smith', 'title': null },
{ 'id': 4, 'name': 'Susan Smith', 'title': 'Dev Mgr' },
{ 'id': 6, 'name': 'Jane Smith', 'title': 'Software Eng 2'}
>>
}
}
Notice that the employees is nested within hr.
The delimiters << ... >> denote that the data
is an unordered collection (also known as bag), as is the case
with SQL tables. That is, there is no order between the three tuples.
Single-line comments start with -- and end at the end of the line.
A very different kind of data source may lead to the same PartiQL dataset. For example, a set of JSON files that contain the following JSON objects
{
"hr" : {
"employees": [
{ "id": 3, "name": "Bob Smith", "title": null },
{ "id": 4, "name": "Susan Smith", "title": "Dev Mgr" },
{ "id": 6, "name": "Jane Smith", "title": "Software Eng 2"}
]
}
}
will likely be abstracted by a PartiQL-supporting
implementation into the identical PartiQL abstraction with the
hr.employees table.
The JSON value attached to employee is an ordered
list. PartiQL implementations may provide their own mappings from popular
data formats, e.g., CSV, TSV, JSON, Ion etc., to the PartiQL data model and/or allow clients
to implements their own mappings.
Remark: You will keep noticing the similarity of the PartiQL notation with the JSON notation. Notice also the subtle differences: In the interest of SQL compatibility, a PartiQL literal is single-quoted, while JSON literals are double-quoted.
Remark: You may conceptually think that a deserializer inputs JSON and outputs the PartiQL data set. But do not assume that the query processing of a PartiQL implementation will have to actually parse and abstract into PartiQL each and every bit of the underlying data storage.
Back to our query
SELECT e.id,
e.name AS employeeName,
e.title AS title
FROM hr.employees e
WHERE e.title = 'Dev Mgr'
Instead of a SQL result set, evaluating the query in PartiQL produces:
<<
{
'id': 4,
'employeeName': 'Susan Smith',
'title': 'Dev Mgr'
}
>>
---
OK!
the result remains the same, no matter whether hr.employees is a
SQL table or a JSON file. All that is needed is an
association between the name hr.employees and the PartiQL abstraction of
the data.
In the same spirit, the same PartiQL abstraction may come from a CSV
file or a Parquet file, a format that has gained big traction, thanks to
the efficient way in which it stores data. Again, the same query makes
perfect sense, regardless of what exactly was the storage format behind
hr.employees.
-
PartiQL data sets look very much like JSON.
What are the differences? Indeed, PartiQL adopts the tuple/object and array notation of JSON. However, the PartiQL string literals are denoted by single quotes. Importantly, the scalar types of PartiQL are those of SQL, not just strings, numbers and booleans, as in JSON.
-
Do implementations need to have a catalog?
If queries refer to names, a catalog logically validates whether the name exists or not. However, we will also see PartiQL queries that refer to no names.
SQL-92 only has tables that have tuples that contain scalar values. A key feature of many modern formats is nested data. That is, attributes whose values may themselves be tables (i.e., collections of tuples), or may be arrays of scalars, or arrays of arrays and many other combinations. Let's take a closer look at PartiQL's features (SQL extensions) that allow us to work with nested data.
We also include sections titled "Use Case". Such "Use Case" sections do not introduce additional features. They merely show how to combine the few novel PartiQL features with standard SQL features in order to solve a large number of problems.
Let's now add the nested attribute projects into the data set.
{
'hr': {
'employeesNest': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [ { 'name': 'AWS Redshift Spectrum querying' },
{ 'name': 'AWS Redshift security' },
{ 'name': 'AWS Aurora security' }
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'projects': [ { 'name': 'AWS Redshift security' } ]
}
>>
}
}
Notice that the value of 'projects' is an array. Arrays are denoted by
[ ... ] with array elements separated by commas. In our example the array
happens to be an array of tuples. We will see that arrays may be arrays
of anything, not just arrays of tuples.
The following query finds the names of employees who work on projects that contain
the string 'security' and outputs them along with the name of the
'security' project. Notice that the query has just one extension
over standard SQL --- the e.projects AS p part.
SELECT e.name AS employeeName,
p.name AS projectName
FROM hr.employeesNest AS e,
e.projects AS p
WHERE p.name LIKE '%security%'
The output of our query is
<<
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Redshift security'
},
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Aurora security'
},
{
'employeeName': 'Jane Smith',
'projectName': 'AWS Redshift security'
}
>>
---
OK!
The extension over SQL is the FROM clause item e.projects AS p.
Standard SQL would attempt to find a schema named e with a table
projects and since in our example there isn't an e.projects
table, the query would fail. In contrast, PartiQL recognizes
e.projects to refer to the projects attribute of e.
Once we allow this extension, the semantics are alike SQL's. The alias
(also called variable in PartiQL) e gets bound to each employee, in
turn. For each employee, the variable p gets bound to each
project of the employee, in turn. Thus the query's meaning, like SQL,
is
foreach employee tuple
efromhr.employeesNestforeach project tuplepfrome.projectsifp.name LIKE '%security%'outpute.name AS employeeName, p.name AS projectName
Notice that our query involved variables that were ranging over nested
collections (p in the example), along with variables that were
ranging over tables (e in the example), as standard SQL aliases do.
All variables, no matter what they range over, can be used wherever in
the FROM, WHERE, SELECT clauses as we will see in the examples that follow.
-
Can I only unnest arrays of tuples?
No, anything can be unnested. For example, arrays of scalars, etc.
-
Does
e.projects AS phave to appear in the sameFROMclause that definese?No. For example, see below the use cases that involve subqueries. There, the
eandpare defined in separateFROMclauses. -
How could I force
e.projectsto refer to the nested attributeprojectseven if there were a schema namedewith a tableprojects?Use the syntax
@e.projects. Recall, in the absence of the@, in the interest of SQL compatibility, PartiQL will first attempt to dereference thee.projectsagainst the catalog. -
SQL allows me to avoid writing an explicit alias
ewhen I write, say,e.name. Can I avoid writing theein PartiQL as well?SQL allows us to avoid writing aliases (variables) when the schema of the tables allows correct dereferencing. PartiQL does the same. However, recall, a schema is not necessary for a PartiQL data set. Indeed, our example has not assumed a schema. In the absence of a schema, you cannot omit the aliases (variables). For example, if you write just
nameand there is no schema, PartiQL cannot tell whether you mean employee name or project name. Thus you need to explicitly write the alias (variable).There is one exception to this rule: If your query has a single item in its
FROMclause, you can omit the alias (variable). Eg, you can writeSELECT name FROM hr.employeesNest
In this case it is apparent that
namemay only be an employee name and thus PartiQL allows you to not provide an alias (variable).Nevertheless, for clarity we recommend that you always use aliases (variables) and this is what this tutorial does.
-
If there is a schema, can I avoid writing the alias
p?No. The
phas to be written in order to denote the iteration over the projects.
In this section, we simply present an alternate way to express and think about unnesting collections.
One may think that the FROM clause of the
example executes, in a sense, a JOIN between employees and projects.
If it helps you to think in terms of JOIN, you may replace the comma
with JOIN. That is, the following two queries are equivalent.
+-----------------------------------+-----------------------------------------+
| SELECT e.name AS employeeName, | SELECT e.name AS employeeName, |
| p.name AS projectName | p.name AS projectName |
| FROM hr.employeesNest AS e, | FROM hr.employeesNest AS e CROSS JOIN |
| e.projects AS p | e.projects AS p |
| WHERE p.name LIKE '%security%' | WHERE p.name LIKE '%security%' |
+-----------------------------------+-----------------------------------------+
Assume that we want to write a query that returns as a bag of
tuples the entire employee and project information from
hr.employeesNest. The query result we want is this bag of tuples
with attributes id, employeeName, title and projectName:
<<
{
'id': 3,
'employeeName': 'Bob Smith',
'title': NULL,
'projectName': 'AWS Redshift Spectrum querying'
},
{
'id': 3,
'employeeName': 'Bob Smith',
'title': NULL,
'projectName': 'AWS Redshift security'
},
{
'id': 3,
'employeeName': 'Bob Smith',
'title': NULL,
'projectName': 'AWS Aurora security'
},
{
'id': 4,
'employeeName': 'Susan Smith',
'title': 'Dev Mgr'
},
{
'id': 6,
'employeeName': 'Jane Smith',
'title': 'Software Eng 2',
'projectName': 'AWS Redshift security'
}
>>
---
OK!
Notice that there is a 'Susan Smith' tuple in the result, despite the
fact that Susan has no project. Susan's projectName is null.
We can obtain this result by combining employees and projects using the
LEFT JOIN operator, as follows:
SELECT e.id AS id,
e.name AS employeeName,
e.title AS title,
p.name AS projectName
FROM hr.employeesNest AS e LEFT JOIN e.projects AS p ON true
The semantics of this query can be thought of as
foreach employee tuple `e` from `hr.employeesNest`
if the `e.projects` is an empty collection then *// this part is special about LEFT JOINs*
output `e.id AS id`, `e.name AS employeeName`, `e.title AS title`
and output a `null AS projectName`
else *// the following part is identical to plain (inner) JOINs*
foreach project tuple `p` from `e.projects`
output `e.id AS id`, `e.name AS employeeName`, `e.title AS title`
The following use cases employ the unnesting features, which we have already discussed, in new use cases. A lesson that emerges is that we can use variables (SQL aliases) that range over nested data as if they were standard SQL aliases. This realization gives us the power to solve a great number of use cases just by combining the unnesting features with features we already know from standard SQL.
In our first use case we want a query that returns the names of the
employees that are involved in a project that contains the word
'security'. The solution employs SQL's "EXISTS (subquery)"
feature, along with unnesting:
SELECT e.name AS employeeName
FROM hr.employeesNest AS e
WHERE EXISTS ( SELECT *
FROM e.projects AS p
WHERE p.name LIKE '%security%')
returns
<<
{
'employeeName': 'Bob Smith'
},
{
'employeeName': 'Jane Smith'
}
>>
---
OK!
In the second use case we want a query that outputs the names of the
employees that have more than one security project and
we are aware of a key for employees (e.g., an attribute
that is guaranteed to have a unique value for each employee).
We can find the requested employees by utilizing a combination of
GROUP BY and HAVING. In our example, let's assume that the
id attribute is a primary key for the employees. Then we could find
the employees with more than one security project with this query:
We could also have used the > operator with the subquery's result, but a current issue with the implementation currently prevents us from doing so.
SELECT e.name AS employeeName
FROM hr.employeesNest e,
e.projects AS p
WHERE p.name LIKE '%security%'
GROUP BY e.id, e.name
HAVING COUNT(*) > 1
which returns
<<
{
'employeeName': 'Bob Smith'
}
>>
---
OK!
Next, let's find how many querying projects (that is, projects whose name contains the word 'querying') each employee has.
Making the same asssumption as before, that id is a key for employees, we can solve
the problem with the query
SELECT e.name AS employeeName,
COUNT(p.name) AS queryProjectsNum
FROM hr.employeesNest e LEFT JOIN e.projects AS p ON p.name LIKE '%querying%'
GROUP BY e.id, e.name
that returns
<<
{
'employeeName': 'Bob Smith',
'queryProjectsNum': 1
},
{
'employeeName': 'Susan Smith',
'queryProjectsNum': 0
},
{
'employeeName': 'Jane Smith',
'queryProjectsNum': 0
}
>>
---
OK!
Notice this query's result includes Susan Smith and Jane Smith, who have no querying projects.
A value may also be a tuple -- also called object and struct in many models and formats. For example, the project value in the following tuples is always a tuple with project name and project org.
{
'hr': {
'employeesWithTuples': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'project': {
'name': 'AWS Redshift Spectrum querying',
'org': 'AWS'
}
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'project': {
'name': 'AWS Redshift security',
'org': 'AWS'
}
}
>>
}
}
PartiQL's multistep paths enable navigating within tuples. For example, the following query finds AWS projects and outputs the project name and employee name.
SELECT e.name AS employeeName,
e.project.name AS projectName
FROM hr.employeesWithTuples e
WHERE e.project.org = 'AWS'
The result is
<<
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Redshift Spectrum querying'
},
{
'employeeName': 'Jane Smith',
'projectName': 'AWS Redshift security'
}
>>
---
OK!
The previous examples have shown nested attributes that were arrays of tuples. It need not be the case that the nested attributes are collections of tuples. They may just as well be arrays of scalars, arrays of arrays, or any combination of data that one can create by composing scalars, tuples and arrays. You need not learn a different set of query language features for each case. The unnesting features, which we have already seen, are sufficient.
The list of projects associated with each employee in
hr.employeesNest could have been simply a list of project name
strings. Replacing the nested tuples with plain strings gives us
{
'hr': {
'employeesNestScalars': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [
'AWS Redshift Spectrum querying',
'AWS Redshift security',
'AWS Aurora security'
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'projects': [ 'AWS Redshift security' ]
}
>>
}
}
Let us repeat the previous use cases on the revised employee data.
The following query finds the names of employees who work on projects
that contain the string 'security' and outputs them along with the name
of the 'security' project.
SELECT e.name AS employeeName,
p AS projectName
FROM hr.employeesNestScalars AS e,
e.projects AS p
WHERE p LIKE '%security%'
The preceding query returns
<<
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Redshift security'
},
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Aurora security'
},
{
'employeeName': 'Jane Smith',
'projectName': 'AWS Redshift security'
}
>>
---
OK!
The variable p ranges (again) over the content of e.projects. In
this case, since e.projects has strings (as opposed to tuples), the
variable p binds each time to a project name string. Thus, this
query can be thought of as executing the following snippet.
foreach employee tuple `e` from `hr.employeesNestScalars`
foreach project `p` from `e.projects`
if the string `p` matches `'%security%'`
output `e.name AS employeeName` and the string `p AS projectName`
Arrays may also contain arrays, directly, without intervening tuples, as
in the matrices data set.
{
'matrices': <<
{
'id': 3,
'matrix': [
[2, 4, 6],
[1, 3, 5, 7],
[9, 0]
]
},
{
'id': 4,
'matrix': [
[5, 8],
[ ]
]
}
>>
}
The following query finds every even number and outputs the even number
and the id of the tuple where it was found.
SELECT t.id AS id,
x AS even
FROM matrices AS t,
t.matrix AS y,
y AS x
WHERE x % 2 = 0
The preceding query returns
<<
{
'id': 3,
'even': 2
},
{
'id': 3,
'even': 4
},
{
'id': 3,
'even': 6
},
{
'id': 3,
'even': 0
},
{
'id': 4,
'even': 8
}
>>
---
OK!
Informally the query's evaluation can be thought of as
foreach tuple `t` from `matrices`
foreach array `y` from `t.matrix`
foreach number `x` from `y`
if `x` is even then
output `t.id AS id` and `x AS even`
Literals of the PartiQL query language correspond to the types in the PartiQL data model:
-
scalars, including
nullwhich follow the SQL syntax when applicable. For example:-
5 -
'foo'
-
-
tuples, denoted by
{...}with tuple elements separated by,(also known as structs and/or objects in many formats and other data models){ 'id' : 3, 'arr': [1, 2] }
-
arrays, denoted by
[...]with array elements separated by,[ 1, 'foo' ]
-
bags, denoted by
<< ... >>with bag elements separated by a,<< 1, 'foo'>>
Notice that in the spirit of the PartiQL data model, literals compose freely and any kind of literal may appear within any tuple, array and bag literal, eg.,
{
'id': 3,
'matrix': [
[2, 4, 6],
'NA'
]
}
Many formats do not require a schema that describes the data -- that is schemaless data. In such cases it is possible to have various "heterogeneities" in the data:
-
One tuple may have an attribute
xwhile another tuple may not have this attribute -
In one tuple of the collection an attribute
xmay be of one type, e.g., string, while in another tuple of the same collection the same attributexmay be of a different type -- e.g, array. -
The elements of a collection (be it a bag or array) can be heterogeneous (not have the same type). For example, the first element may be a string, the second one may be an integer and the third one an array.
-
Generally, any composition is possible as we can bundle heterogeneous elements in arrays and bags.
Heterogeneities are not particular to schemaless. Schemas may allow for
heterogeneity in the types of the data. For example, one of the Hive
data types is the union type, which allows a value to belong to any one of a
list of types. Consider the following schema whose projects attribute may be
either a string or an array of strings
CREATE TABLE employeesMixed(
id: INT,
name: STRING,
title: STRING,
projects: UNIONTYPE<STRING, ARRAY<STRING>>
);A collection of PartiQL tuples that follows this schema could be
{
'hr': {
'employeesMixed1': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [
'AWS Redshift Spectrum querying',
'AWS Redshift security',
'AWS Aurora security'
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'projects': 'AWS Redshift security'
}
>>
}
}
Thus we see that data may have heterogeneities --- regardless of whether they are described by a schema or not. PartiQL tackles heterogeneous data in ways that we will see in the next use cases and feature presentations.
Let's go back to the hr.employees table (that is, bag of tuples).
Bob Smith has no title and, as is typical in SQL, the lack of title is
modeled with the null value.
{
'hr': {
'employees': <<
{ 'id': 3, 'name': 'Bob Smith', 'title': null }
{ 'id': 4, 'name': 'Susan Smith', 'title': 'Dev Mgr' }
{ 'id': 6, 'name': 'Jane Smith', 'title': 'Software Eng 2'}
>>
}
}
Nowadays, many semi-structured formats allow users to represent "missing" information in two ways.
- The first way is by use of
null. - The second kind is the plain absence of the attribute from the tuple.
That is, we can represent the fact that Bob Smith has no title
by simply having no title attribute in the 'Bob Smith' tuple:
{
'hr': {
'employeesWithMissing': <<
{ 'id': 3, 'name': 'Bob Smith' }, -- no title in this tuple
{ 'id': 4, 'name': 'Susan Smith', 'title': 'Dev Mgr' },
{ 'id': 6, 'name': 'Jane Smith', 'title': 'Software Eng 2'}
>>
}
}
PartiQL does not argue about when to use nulls and when to use
"missing". Myriads of datasets already use one of the two or both.
However, PartiQL enables queries to distinguish between null and
missing values, and also enables query results that have nulls and
missing values. Indeed, PartiQL makes it very easy to propagate source
data nulls as query result nulls and source data missing attributes into
result missing attributes.
Consider again this PartiQL query, which happens to also be an SQL query.
SELECT e.id,
e.name AS employeeName,
e.title AS title
FROM hr.employeesWithMissing AS e
WHERE e.title = 'Dev Mgr'
What will happen when the query goes over the Bob Smith tuple, which has
no title?
The first step to answering this question is understanding the result of
the path e.title when the alias (variable) e binds to the tuple
{ 'id': 3, 'name': 'Bob Smith' }. In more basic terms, what is the
result of the expression { 'id': 3, 'name': 'Bob Smith' }.title ?
PartiQL says that it is the special value MISSING. MISSING
behaves very similar to null.
If a function (including infix functions like =) inputs a
MISSING the function's result is NULL. In the case of the example,
this means that the WHERE clause e.title='Dev Mgr' will evaluate
to NULL when e binds to { 'id': 3, 'name': 'Bob Smith' }
and, as usual in SQL, the WHERE clause fails when it does not
evaluate to true. Thus the output will be
<<
{
'id': 4,
'employeeName': 'Susan Smith',
'title': 'Dev Mgr'
}
>>
---
OK!
What would happen if a missing attribute or, more generally, an
expression returning MISSING appears in the SELECT?
SELECT e.id,
e.name AS employeeName,
e.title AS outputTitle
FROM hr.employeesWithMissing AS e
The query will output one tuple for each employee. When it outputs the
Bob Smith tuple, the e.title will evaluate to NULL and then
the output tuple will not have an outputTitle attribute.
<<
{
'id': 3,
'employeeName': 'Bob Smith'
},
{
'id': 4,
'employeeName': 'Susan Smith',
'outputTitle': 'Dev Mgr'
},
{
'id': 6,
'employeeName': 'Jane Smith',
'outputTitle': 'Software Eng 2'
}
>>
---
OK!
The same treatment of MISSING would happen if, say, we had this
query that converts titles to capital letters:
SELECT e.id,
e.name AS employeeName,
UPPER(e.title) AS outputTitle
FROM hr.employeesWithMissing AS e
Again, the e.title will evaluate to MISSING for 'Bob Smith', the
UPPER(e.title) is then UPPER(MISSING) and also evaluates to NULL.
Thus the result will be:
<<
{
'id': 3,
'employeeName': 'Bob Smith',
'outputTitle': NULL
},
{
'id': 4,
'employeeName': 'Susan Smith',
'outputTitle': 'DEV MGR'
},
{
'id': 6,
'employeeName': 'Jane Smith',
'outputTitle': 'SOFTWARE ENG 2'
}
>>
---
OK!
A PartiQL variable (called alias in SQL) can bind to data of different types during a query's evaluation. This is unlike SQL where the variables always bind to tuples. It is even different from what happened in Use Case: Unnesting Arrays of Scalars and what happened in Use Case: Unnesting Arrays of Arrays.
In the first use case, the PartiQL variable p
happened to always bind to a string (given the particular sample data of
the example). In the second use case, the PartiQL variable y was
always bound to an array (again, given the particular sample data of the
example).
To make the case for variables that bind to different types, consider
the following twist in the employeesNest data set. Some of the
elements of the projects array are plain strings and some are
tuples. Even the employee tuples do not always have the same attributes.
{
'hr': {
'employeesMixed2': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [
{ 'name': 'AWS Redshift Spectrum querying' },
'AWS Redshift security',
{ 'name': 'AWS Aurora security' }
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'projects': [ 'AWS Redshift security']
}
>>
}
}
This query on hr.employeesMixed2 produces employee name -- employee
project pairs.
SELECT e.name AS employeeName,
CASE WHEN (p IS TUPLE) THEN p.name
ELSE p END AS projectName
FROM hr.employeesMixed2 AS e,
e.projects AS p
Notice the sub-expression (p IS TUPLE). The IS operator can be used
to check a value against its type at evaluation time.
Notice also that the variable p binds to different types.
In general, the FROM clause of a query binds its variables (aliases)
to data. The variables need not bind to data that have the same
types. Each binding is fed to the SELECT clause, which evaluates its
expressions.
This table shows each variables' binding produced by the FROM clause
and the corresponding tuple output by the SELECT clause.
+-----------------------+-----------------------+-----------------------+
| Variable `e` | Variable `p` | Result tuple |
+=======================+=======================+=======================+
| { 'id': 3, | { 'name': 'AWS | { |
| | Redshift Spectrum | |
| 'name': 'Bob Smith', | querying' } | 'employeeName': 'Bob |
| | | Smith', |
| 'title': null, | | |
| | | 'projectName': 'AWS |
| 'projects': [ { | | Redshift Spectrum |
| 'name': 'AWS Redshift | | querying' |
| Spectrum querying' }, | | |
| | | } |
| 'AWS Redshift | | |
| security', | | |
| | | |
| { 'name': 'AWS Aurora | | |
| security' } | | |
| | | |
| ] | | |
| | | |
| } | | |
+-----------------------+-----------------------+-----------------------+
| { 'id': 3, | 'AWS Redshift | { |
| | security' | |
| 'name': 'Bob Smith', | | 'employeeName': 'Bob |
| | | Smith', |
| 'title': null, | | |
| | | 'projectName': 'AWS |
| 'projects': [ { | | Redshift security' |
| 'name': 'AWS Redshift | | |
| Spectrum querying' }, | | } |
| | | |
| 'AWS Redshift | | |
| security', | | |
| | | |
| { 'name': 'AWS Aurora | | |
| security' } | | |
| | | |
| ] | | |
| | | |
| } | | |
+-----------------------+-----------------------+-----------------------+
| { 'id': 3, | { 'name': 'AWS Aurora | { |
| | security' } | |
| 'name': 'Bob Smith', | | 'employeeName': 'Bob |
| | | Smith', |
| 'title': null, | | |
| | | 'projectName': 'AWS |
| 'projects': \[ { | | Aurora security' |
| 'name': 'AWS Redshift | | |
| Spectrum querying' }, | | } |
| | | |
| 'AWS Redshift | | |
| security', | | |
| | | |
| { 'name': 'AWS Aurora | | |
| security' } | | |
| | | |
| \] | | |
| | | |
| } | | |
+-----------------------+-----------------------+-----------------------+
| { 'id': 6, | 'AWS Redshift | { |
| | security' | |
| 'name': 'Jane Smith', | | 'employeeName': |
| | | 'Jane Smith', |
| 'projects': \[ 'AWS | | |
| Redshift security' \] | | 'projectName': 'AWS |
| | | Redshift security' |
| } | | |
| | | } |
+-----------------------+-----------------------+-----------------------+
SQL allows us to order the output of a query using the ORDER BY
clause. However, the SQL data model does not recognize order in the
input data. In contrast, many of the new data formats feature arrays;
the arrays' elements have an order. We may want to find an array element
by its index or, we may want to find the positions of certain
elements in their arrays.
Let's consider again the dataset hr.employeesNest.
{
'hr': {
'employeesNest': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [ { 'name': 'AWS Redshift Spectrum querying' },
{ 'name': 'AWS Redshift security' },
{ 'name': 'AWS Aurora security' }
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'projects': [ { 'name': 'AWS Redshift security' } ]
}
>>
}
}
The projects attribute is an array of tuples; that is, each tuple
has an ordinal associated with it. The following query returns each
employee name, along with the first project of the employee.
SELECT e.name AS employeeName,
e.projects[0].name AS firstProjectName
FROM hr.employeesNest AS e
The query returns
<<
{
'employeeName': 'Bob Smith',
'firstProjectName': 'AWS Redshift Spectrum querying'
},
{
'employeeName': 'Susan Smith'
},
{
'employeeName': 'Jane Smith',
'firstProjectName': 'AWS Redshift security'
}
>>
---
OK!
Technically, the structure [<number>] is a kind of path step.
For example, notice the 4-step path e.projects[0].name. When e
is bound to the first tuple of hr.employeesNest, then the path
e.projects results into the array
[
{ 'name': 'AWS Redshift Spectrum querying' },
{ 'name': 'AWS Redshift security' },
{ 'name': 'AWS Aurora security' }
]
Consequently applying the [0] step on e.projects (that is,
evaluating e.projects[0]) leads to {'name': 'AWS Redshift Spectrum querying'}. Finally, evaluating the .name step on
e.projects[0] (that is, evaluating e.projects[0].name) leads
to 'AWS Redshift Spectrum querying'.
Let's assume that each employees' projects are sorted in priority order.
The following query finds the names of each employee
involved in a security project, the security project, and, its index in
the projects array.
SELECT e.name AS employeeName,
p.name AS projectName,
o AS projectPriority
FROM hr.employeesNest AS e,
e.projects AS p AT o
WHERE p.name LIKE '%security%'
Notice the new feature: AT o. While p ranges over the elements
of the array e.projects, the variable o is assigned to the index of
the element in the array. The query returns:
<<
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Redshift security',
'projectPriority': 1
},
{
'employeeName': 'Bob Smith',
'projectName': 'AWS Aurora security',
'projectPriority': 2
},
{
'employeeName': 'Jane Smith',
'projectName': 'AWS Redshift security',
'projectPriority': 0
}
>>
---
OK!
Many queries need to range over and collect the attribute name/value pairs of tuples or the key/value pairs of maps.
Consider this dataset that provides the closing prices of multiple ticker symbols.
{
'closingPrices': <<
{ 'date': '4/1/2019', 'amzn': 1900, 'goog': 1120, 'fb': 180 },
{ 'date': '4/2/2019', 'amzn': 1902, 'goog': 1119, 'fb': 183 }
>>
}
The following query unpivots the stock ticker/price pairs.
SELECT c."date" AS "date",
sym AS "symbol",
price AS price
FROM closingPrices AS c,
UNPIVOT c AS price AT sym
WHERE NOT sym = 'date'
Notice the use of " in this query. The double quotes allow us to
disambiguate from date the keyword and "date" the identifier.
Double quotes can also specify case sensitivity for attribute lookups.
The query returns
<<
{
'date': '4/1/2019',
'symbol': 'amzn',
'price': 1900
},
{
'date': '4/1/2019',
'symbol': 'goog',
'price': 1120
},
{
'date': '4/1/2019',
'symbol': 'fb',
'price': 180
},
{
'date': '4/2/2019',
'symbol': 'amzn',
'price': 1902
},
{
'date': '4/2/2019',
'symbol': 'goog',
'price': 1119
},
{
'date': '4/2/2019',
'symbol': 'fb',
'price': 183
}
>>
---
OK!
Unpivoting tuples enables the use of attribute names as if they were data. For example, it becomes easy to compute the average price for each symbol as
SELECT sym AS "symbol",
AVG(price) AS avgPrice
FROM closingPrices c,
UNPIVOT c AS price AT sym
WHERE NOT sym = 'date'
GROUP BY sym
which returns
<<
{
'symbol': 'amzn',
'avgPrice': 1901
},
{
'symbol': 'fb',
'avgPrice': 181.5
},
{
'symbol': 'goog',
'avgPrice': 1119.5
}
>>
---
OK!
Pivoting turns a collection into a tuple. For example, consider the collection
{
'todaysStockPrices': <<
{ 'symbol': 'amzn', 'price': 1900},
{ 'symbol': 'goog', 'price': 1120},
{ 'symbol': 'fb', 'price': 180 }
>>
}
Then the following PIVOT query
PIVOT sp.price AT sp."symbol"
FROM todaysStockPrices sp
produces the tuple
{
'amzn': 1900,
'goog': 1120,
'fb': 180
}
---
OK!
Notice that the PIVOT query looks like a SELECT-FROM-WHERE-...
query except that instead of a SELECT clause it has a PIVOT <value expression> AT <attribute expression>. Note also that the
PIVOT query does not return a collection of tuples: rather
it literally returns a tuple value.
(This example also uses the grouping features of PartiQL, Creating
Nested Results with GROUP BY ... GROUP AS.)
Let us generalize the previous case of pivoting. We have a table of stock prices
{
'stockPrices':<<
{ 'date': '4/1/2019', 'symbol': 'amzn', 'price': 1900},
{ 'date': '4/1/2019', 'symbol': 'goog', 'price': 1120},
{ 'date': '4/1/2019', 'symbol': 'fb', 'price': 180 },
{ 'date': '4/2/2019', 'symbol': 'amzn', 'price': 1902},
{ 'date': '4/2/2019', 'symbol': 'goog', 'price': 1119},
{ 'date': '4/2/2019', 'symbol': 'fb', 'price': 183 }
>>
}
and we want to pivot it into a collection of tuples, where each tuple
has all the symbol:price pairs for a date, as follows
<<
{
'date': date(4/1/2019),
'prices': {'amzn': 1900, 'goog': 1120, 'fb': 180}
},
{
'date': date(4/2/2019),
'prices': {'amzn': 1902, 'goog': 1119, 'fb': 183}
}
>>
The following query first creates one group datesPrices for each date.
Then the PIVOT subquery pivots the group into the tuple prices.
SELECT sp."date" AS "date",
(PIVOT dp.sp.price AT dp.sp."symbol"
FROM datesPrices as dp ) AS prices
FROM StockPrices AS sp GROUP BY sp."date" GROUP AS datesPrices
For example, the datesPrices collection, returned from GROUP AS for
sp.date = date(4/1/2019) is
'datesPrices': <<
{
'sp': {
'date': '4/1/2019',
'symbol': 'amzn',
'price': 1900
}
},
{
'sp': {
'date': '4/1/2019',
'symbol': 'goog',
'price': 1120
}
},
{
'sp': {
'date': '4/1/2019',
'symbol': 'fb',
'price': 180
}
}
>>
PartiQL allows queries that create nested results as well as queries that create heterogeneous results.
Let's consider again the dataset hr.employeesNestScalars:
{
'hr': {
'employeesNestScalars': <<
{
'id': 3,
'name': 'Bob Smith',
'title': null,
'projects': [
'AWS Redshift Spectrum querying',
'AWS Redshift security',
'AWS Aurora security'
]
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'projects': []
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'projects': [ 'AWS Redshift security' ]
}
>>
}
}
The following query outputs each tuple of hr.employeesNestScalars,
except that instead of all projects each tuple has only the security
projects of the employee. The important new feature here is the
SELECT VALUE <expression>.
SELECT e.id AS id,
e.name AS name,
e.title AS title,
( SELECT VALUE p
FROM e.projects AS p
WHERE p LIKE '%security%'
) AS securityProjects
FROM hr.employeesNestScalars AS e
The result is
<<
{
'id': 3,
'name': 'Bob Smith',
'title': NULL,
'securityProjects': <<
'AWS Redshift security',
'AWS Aurora security'
>>
},
{
'id': 4,
'name': 'Susan Smith',
'title': 'Dev Mgr',
'securityProjects': <<>>
},
{
'id': 6,
'name': 'Jane Smith',
'title': 'Software Eng 2',
'securityProjects': <<
'AWS Redshift security'
>>
}
>>
---
OK!
A SELECT VALUE <expression> query (or subquery, as in this
example) returns a collection of whatever the <expression>
evaluates to.
Notice the difference from SQL's SELECT, which always produces
tuples. If a SQL SELECT appears as a subquery, then the context of
the subquery designates whether the subquery's result should be coerced
into a scalar (e.g., when 5 = <subquery>), coerced into a
collection of scalars (e.g., when 5 IN <subquery>), etc. None of
this applies to SELECT VALUE, which produces a collection and this
collection is not coerced.
Another pattern of creating nested results in PartiQL is via the GROUP AS extension to SQL's GROUP BY. This pattern is more efficient and
more intuitive than the use of nested SELECT VALUE queries when the
required nesting is not following the nesting of the input. (The example
in Creating Nested Results with SELECT VALUE Queries is one where
the nesting in the output follows the nesting of the input and thus, an
intuitive solution does not involve GROUP BY.)
The following query outputs each security project found in
hr.employeesNestScalars along with the list of employee names that
work on the project.
SELECT p AS projectName,
( SELECT VALUE v.e.name
FROM perProjectGroup AS v ) AS employees
FROM hr.employeesNestScalars AS e JOIN e.projects AS p ON p LIKE '%security%'
GROUP BY p GROUP AS perProjectGroup
The result is
<<
{
'projectName': 'AWS Aurora security',
'employees': <<
'Bob Smith'
>>
},
{
'projectName': 'AWS Redshift security',
'employees': <<
'Bob Smith',
'Jane Smith'
>>
}
>>
---
OK!
The GROUP AS generalizes SQL's GROUP BY by making the formulated
groups available in their entirety to the query's SELECT and
HAVING clauses. Contrast with SQL's GROUP BY, where the
SELECT and HAVING clauses can have aggregate functions over
grouped columns but they cannot get access to the individual values of
the grouped columns.
To better understand the workings of GROUP BY ... GROUP AS it is
best to think of PartiQL queries as a pipeline of clauses, starting with
the FROM, continuing with the GROUP BY and finishing with the
SELECT. Each clause is a function that inputs data and outputs data.
In that sense, the GROUP BY ... GROUP AS is a function that inputs
the result of the FROM and outputs its result to the SELECT.
The following query (conceptually) produces the output of the FROM
clause.
SELECT e AS e, p AS p
FROM hr.employeesNestScalars AS e JOIN e.projects AS p ON p LIKE '%security%'We see that the FROM delivers the collection of tuples consisting of
an employee e and a project p that were output by the FROM
clause, i.e., the LEFT JOIN. This is like SQL's FROM semantics.
+-----------------------------------+-----------------------------------+
| Variable `e` | Variable `p` |
+===================================+===================================+
| { 'id': 3, | 'AWS Redshift security' |
| 'name': 'Bob Smith', | |
| 'title': null, | |
| 'projects': [ 'AWS Redshift | |
| Spectrum querying', | |
| 'AWS Redshift security', | |
| 'AWS Aurora security' | |
| ] | |
| } | |
+-----------------------------------+-----------------------------------+
| { 'id': 3, | 'AWS Aurora security' |
| 'name': 'Bob Smith', | |
| 'title': null, | |
| 'projects': [ 'AWS Redshift | |
| Spectrum querying', | |
| 'AWS Redshift security', | |
| 'AWS Aurora security' | |
| ] | |
| } | |
+-----------------------------------+-----------------------------------+
| { 'id': 6, | 'AWS Redshift security' |
| 'name': 'Jane Smith', | |
| 'title': 'Software Eng 2', | |
| 'projects': [ 'AWS Redshift | |
| security' ] | |
| } | |
+-----------------------------------+-----------------------------------+
Then the GROUP BY ... GROUP AS ... can be thought of as outputting a
table that has one column for each group-by expression (i.e., each
security project p) and a last column perProjectGroup whose
value (conceptually) is the collection of employee/project e/p
tuples that correspond to the group-by expression p. Thus the
GROUP BY ... GROUP AS ... output is the table
+-----------------------------------+-----------------------------------+
| `p` | `perProjectGroup` |
+===================================+===================================+
| 'AWS Redshift security' | << |
| | { e: { 'id': 3, 'name': 'Bob |
| | Smith', ... }, p: 'AWS Redshift |
| | security' }, |
| | |
| | { e: { 'id': 6, 'name': 'Jane |
| | Smith', ... }, p: 'AWS Redshift |
| | security' } |
| | >> |
+-----------------------------------+-----------------------------------+
| 'AWS Aurora security' | << |
| | { e: { 'id': 3, 'name': 'Bob |
| | Smith', ...}, p: 'AWS Aurora |
| | security' }, |
| | >> |
+-----------------------------------+-----------------------------------+
Finally the SELECT clause inputs the above and outputs the query
result.
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