perf: add additional covering index to ahb_expressions (#227)

* perf: add additional covering index to `ahb_expressions`

* Update src/fundamend/sqlmodels/expression_view.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* the first arg to Index is the index name, not the first column involved

---------

Co-authored-by: Konstantin <konstantin.klein+github@hochfrequenz.de>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

src/fundamend/sqlmodels/expression_view.py

@@ -9,6 +9,7 @@
 from typing import Optional
 
 from efoli import EdifactFormat, EdifactFormatVersion
+from sqlalchemy import Index
 
 from fundamend.sqlmodels import AhbHierarchyMaterialized, Bedingung
 from fundamend.sqlmodels.anwendungshandbuch import Paket, UbBedingung
@@ -229,6 +230,15 @@ class AhbExpression(SQLModel, table=True):
             "expression",
             name="idx_ahb_expressions_metadata_expression",
         ),
+        Index(
+            # this is to speed up the v_ahb_diff joins
+            "idx_ahb_expressions_covering_v_ahb_diff",
+            "edifact_format_version",
+            "format",
+            "expression",
+            "node_texts",
+            "ahbicht_error_message",
+        ),
     )
     id: uuid.UUID = Field(primary_key=True, default_factory=uuid.uuid4)
     edifact_format_version: EdifactFormatVersion = Field(index=True)