bugfix:(transpile) use static alias for unnesting a struct

sqlglot/dialects/hive.py

@@ -555,7 +555,7 @@ class Generator(generator.Generator):
                 [
                     transforms.eliminate_qualify,
                     transforms.eliminate_distinct_on,
-                    partial(transforms.unnest_to_explode, unnest_using_arrays_zip=False),
+                    partial(transforms.unnest_to_explode),
                     transforms.any_to_exists,
                 ]
             ),

sqlglot/transforms.py

@@ -302,19 +302,13 @@ def unqualify_unnest(expression: exp.Expression) -> exp.Expression:
     return expression
 
 
-def unnest_to_explode(
-    expression: exp.Expression,
-    unnest_using_arrays_zip: bool = True,
-) -> exp.Expression:
+def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
     """Convert cross join unnest into lateral view explode."""
 
     def _unnest_zip_exprs(
         u: exp.Unnest, unnest_exprs: t.List[exp.Expression], has_multi_expr: bool
     ) -> t.List[exp.Expression]:
         if has_multi_expr:
-            if not unnest_using_arrays_zip:
-                raise UnsupportedError("Cannot transpile UNNEST with multiple input arrays")
-
             # Use INLINE(ARRAYS_ZIP(...)) for multiple expressions
             zip_exprs: t.List[exp.Expression] = [
                 exp.Anonymous(this="ARRAYS_ZIP", expressions=unnest_exprs)
@@ -368,6 +362,25 @@ def _udtf_type(u: exp.Unnest, has_multi_expr: bool) -> t.Type[exp.Func]:
                 expression.args["joins"].remove(join)
 
                 alias_cols = alias.columns if alias else []
+
+                """
+                Handle Presto CROSS JOIN UNNEST to LATERAL VIEW EXPLODE for Multiple or No Exploded table column alias.
+
+                Spark/Hive LATERAL VIEW EXPLODE requires only single alias for respective exploded array/struct to be given for unnest ulike trino/presto which can take multiple.
+                https://cwiki.apache.org/confluence/display/Hive/LanguageManual+LateralView
+                https://spark.apache.org/docs/latest/sql-ref-syntax-qry-select-lateral-view.html
+
+                """
+                # Replace multiple alias for single EXPLODE column with single static alias name: `t_struct`
+                if not has_multi_expr and (len(alias_cols) != 1):
+                    alias_cols = ["t_struct"]
+
+                    # [Optional] Do Update the Column reference in AST for table with current alias
+                    if alias:
+                        for column in expression.find_all(exp.Column):
+                            if column.table == alias.name:
+                                column.set("table", "t_struct")
+
                 for e, column in zip(exprs, alias_cols):
                     expression.append(
                         "laterals",
@@ -376,7 +389,7 @@ def _udtf_type(u: exp.Unnest, has_multi_expr: bool) -> t.Type[exp.Func]:
                             view=True,
                             alias=exp.TableAlias(
                                 this=alias.this,  # type: ignore
-                                columns=alias_cols if unnest_using_arrays_zip else [column],  # type: ignore
+                                columns=alias_cols,
                             ),
                         ),
                     )

tests/dialects/test_dialect.py

@@ -1444,6 +1444,34 @@ def test_cross_join(self):
             },
         )
 
+        # UNNEST without column alias
+        self.validate_all(
+            "SELECT * FROM x CROSS JOIN UNNEST(y) AS t",
+            write={
+                "presto": "SELECT * FROM x CROSS JOIN UNNEST(y) AS t",
+                "spark": "SELECT * FROM x LATERAL VIEW EXPLODE(y) t AS t_struct",
+                "databricks": "SELECT * FROM x LATERAL VIEW EXPLODE(y) t AS t_struct",
+            },
+        )
+
+        # UNNEST STRUCT Object into multiple columns, using single alias
+        self.validate_all(
+            "SELECT a, b FROM x CROSS JOIN UNNEST(y) AS t (a, b)",
+            write={
+                "presto": "SELECT a, b FROM x CROSS JOIN UNNEST(y) AS t(a, b)",
+                "spark": "SELECT a, b FROM x LATERAL VIEW EXPLODE(y) t AS t_struct",
+            },
+        )
+
+        # Unnest multiple Expression into respective mapped alias
+        self.validate_all(
+            "SELECT numbers, animals, n, a FROM (SELECT ARRAY(2, 5) AS numbers, ARRAY('dog', 'cat', 'bird') AS animals UNION ALL SELECT ARRAY(7, 8, 9), ARRAY('cow', 'pig')) AS x CROSS JOIN UNNEST(numbers, animals) AS t(n, a)",
+            write={
+                "presto": "SELECT numbers, animals, n, a FROM (SELECT ARRAY[2, 5] AS numbers, ARRAY['dog', 'cat', 'bird'] AS animals UNION ALL SELECT ARRAY[7, 8, 9], ARRAY['cow', 'pig']) AS x CROSS JOIN UNNEST(numbers, animals) AS t(n, a)",
+                "spark": "SELECT numbers, animals, n, a FROM (SELECT ARRAY(2, 5) AS numbers, ARRAY('dog', 'cat', 'bird') AS animals UNION ALL SELECT ARRAY(7, 8, 9), ARRAY('cow', 'pig')) AS x LATERAL VIEW INLINE(ARRAYS_ZIP(numbers, animals)) t AS n, a",
+            },
+        )
+
     def test_lateral_subquery(self):
         self.validate_identity(
             "SELECT art FROM tbl1 INNER JOIN LATERAL (SELECT art FROM tbl2) AS tbl2 ON tbl1.art = tbl2.art"

tests/dialects/test_starrocks.py

@@ -1,4 +1,3 @@
-from sqlglot.errors import UnsupportedError
 from tests.dialects.test_dialect import Validator
 
 
@@ -91,7 +90,7 @@ def test_unnest(self):
                 "spark": r"""SELECT id, t.type, t.scores FROM example_table LATERAL VIEW INLINE(ARRAYS_ZIP(SPLIT(type, CONCAT('\\Q', ';', '\\E')), scores)) t AS type, scores""",
                 "databricks": r"""SELECT id, t.type, t.scores FROM example_table LATERAL VIEW INLINE(ARRAYS_ZIP(SPLIT(type, CONCAT('\\Q', ';', '\\E')), scores)) t AS type, scores""",
                 "starrocks": r"""SELECT id, t.type, t.scores FROM example_table, UNNEST(SPLIT(type, ';'), scores) AS t(type, scores)""",
-                "hive": UnsupportedError,
+                "hive": r"""SELECT id, t.type, t.scores FROM example_table LATERAL VIEW INLINE(ARRAYS_ZIP(SPLIT(type, CONCAT('\\Q', ';', '\\E')), scores)) t AS type, scores""",
             },
         )
 
@@ -100,7 +99,7 @@ def test_unnest(self):
             write={
                 "spark": r"""SELECT id, t.type, t.scores FROM example_table_2 LATERAL VIEW INLINE(ARRAYS_ZIP(SPLIT(type, CONCAT('\\Q', ';', '\\E')), scores)) t AS type, scores""",
                 "starrocks": r"""SELECT id, t.type, t.scores FROM example_table_2 CROSS JOIN LATERAL UNNEST(SPLIT(type, ';'), scores) AS t(type, scores)""",
-                "hive": UnsupportedError,
+                "hive": r"""SELECT id, t.type, t.scores FROM example_table_2 LATERAL VIEW INLINE(ARRAYS_ZIP(SPLIT(type, CONCAT('\\Q', ';', '\\E')), scores)) t AS type, scores""",
             },
         )