Scope the ALTER SESSION parser override to Snowflake

Author: DG47

sqlmesh/core/dialect.py

@@ -569,11 +569,13 @@ def _parse_alter_table_alter(self: Parser) -> t.Optional[exp.Expr]:
     return alter_column
 
 
-# Session parameter names in ALTER SESSION SET / UNSET (e.g. Snowflake's TIMEZONE or QUERY_TAG)
-# are keywords, not identifiers, so engines reject them when quoted: ALTER SESSION SET "TIMEZONE"
-# = 'UTC' is a syntax error in Snowflake. sqlglot parses them as identifiers, which means they get
-# normalized and quoted along with the rest of the statement, so we turn them into vars instead.
-def _parse_alter_session(self: Parser) -> exp.AlterSession:
+# Snowflake session parameter names in ALTER SESSION SET / UNSET (e.g. TIMEZONE or QUERY_TAG) are
+# keywords, not identifiers, so Snowflake rejects them when quoted: ALTER SESSION SET "TIMEZONE" = 'UTC'
+# is a syntax error. sqlglot parses them as identifiers, which means they get normalized and quoted
+# along with the rest of the statement, so we turn them into vars instead. Vars are also left out of
+# case normalization, so a parameter written as query_tag stays lowercase; Snowflake treats parameter
+# names case-insensitively, so this is intentional.
+def _parse_alter_session(self: Snowflake.Parser) -> exp.AlterSession:
     alter_session = self.__parse_alter_session()  # type: ignore
 
     for item in alter_session.expressions:
@@ -1447,7 +1449,7 @@ def extend_sqlglot() -> None:
     _override(Parser, _parse_interval_span)
     _override(Parser, _warn_unsupported)
     _override(Snowflake.Parser, _parse_table_parts)
-    _override(Parser, _parse_alter_session)
+    _override(Snowflake.Parser, _parse_alter_session)
     _override(TSQL.Parser, _parse_alter_table_alter)
     _override(TSQL.Generator, altercolumn_sql)