Feat(exasol): qualify bare stars to facilitate transpilation (#6431)

* chore(exasol): implemented a select preprocessor to qualify bare '*' and add alias in exasol

* chore(exasol): refactored implementation to handle SELECT * queries with multiple sources

* chore(exasol): fixed linting

* chore(exasol): refactored implementation to qualify bare star

* chore(exasol): changed method name and added more test

* chore(exasol): fixed the test  cases using validate_all instead of validate_identity

* chore(exasol): refactored implementation reducing the walk through select_expressions, mutating the original star and fixing normalization issues

Author: nnamdi16

sqlglot/dialects/exasol.py

@@ -20,6 +20,7 @@
 from sqlglot.generator import unsupported_args
 from sqlglot.helper import seq_get
 from sqlglot.tokens import TokenType
+from sqlglot.optimizer.scope import build_scope
 
 if t.TYPE_CHECKING:
     from sqlglot.dialects.dialect import DialectType
@@ -183,6 +184,66 @@ def _substring_index_sql(self: Exasol.Generator, expression: exp.SubstringIndex)
     return self.func("SUBSTR", haystack_sql, direction, length)
 
 
+# https://docs.exasol.com/db/latest/sql/select.htm#:~:text=The%20select_list%20defines%20the%20columns%20of%20the%20result%20table.%20If%20*%20is%20used%2C%20all%20columns%20are%20listed.%20You%20can%20use%20an%20expression%20like%20t.*%20to%20list%20all%20columns%20of%20the%20table%20t%2C%20the%20view%20t%2C%20or%20the%20object%20with%20the%20table%20alias%20t.
+def _qualify_unscoped_star(expression: exp.Expression) -> exp.Expression:
+    """
+    Exasol doesn't support a bare * alongside other select items, so we rewrite it
+    Rewrite: SELECT *, <other> FROM <Table>
+    Into: SELECT T.*, <other> FROM <Table> AS T
+    """
+
+    if not isinstance(expression, exp.Select):
+        return expression
+
+    select_expressions = expression.expressions or []
+
+    def is_bare_star(expr: exp.Expression) -> bool:
+        return isinstance(expr, exp.Star) and expr.this is None
+
+    has_other_expression = False
+    bare_star_expr: exp.Expression | None = None
+    for expr in select_expressions:
+        has_bare_star = is_bare_star(expr)
+        if has_bare_star and bare_star_expr is None:
+            bare_star_expr = expr
+        elif not has_bare_star:
+            has_other_expression = True
+        if bare_star_expr and has_other_expression:
+            break
+
+    if not (bare_star_expr and has_other_expression):
+        return expression
+
+    scope = build_scope(expression)
+
+    if not scope or not scope.selected_sources:
+        return expression
+
+    table_identifiers: list[exp.Identifier] = []
+
+    for source_name, (source_expr, _) in scope.selected_sources.items():
+        ident = (
+            source_expr.this.copy()
+            if isinstance(source_expr, exp.Table) and isinstance(source_expr.this, exp.Identifier)
+            else exp.to_identifier(source_name)
+        )
+        table_identifiers.append(ident)
+
+    qualified_star_columns = [
+        exp.Column(this=bare_star_expr.copy(), table=ident) for ident in table_identifiers
+    ]
+
+    new_select_expressions: list[exp.Expression] = []
+
+    for select_expr in select_expressions:
+        new_select_expressions.extend(qualified_star_columns) if is_bare_star(
+            select_expr
+        ) else new_select_expressions.append(select_expr)
+
+    expression.set("expressions", new_select_expressions)
+    return expression
+
+
 def _add_date_sql(self: Exasol.Generator, expression: DATE_ADD_OR_SUB) -> str:
     interval = expression.expression if isinstance(expression.expression, exp.Interval) else None
 
@@ -467,6 +528,7 @@ def datatype_sql(self, expression: exp.DataType) -> str:
             exp.CommentColumnConstraint: lambda self, e: f"COMMENT IS {self.sql(e, 'this')}",
             exp.Select: transforms.preprocess(
                 [
+                    _qualify_unscoped_star,
                     _add_local_prefix_for_aliases,
                 ]
             ),

tests/dialects/test_exasol.py

@@ -11,6 +11,44 @@ def test_exasol(self):
             'SELECT 1 AS "x"',
         )
 
+    def test_qualify_unscoped_star(self):
+        self.validate_all(
+            "SELECT TEST.*, 1 FROM TEST",
+            read={
+                "": "SELECT *, 1 FROM TEST",
+            },
+        )
+        self.validate_identity(
+            "SELECT t.*, 1 FROM t",
+        )
+        self.validate_identity(
+            "SELECT t.* FROM t",
+        )
+        self.validate_identity(
+            "SELECT * FROM t",
+        )
+        self.validate_identity(
+            "WITH t AS (SELECT 1 AS x) SELECT t.*, 3 FROM t",
+        )
+        self.validate_all(
+            "WITH t1 AS (SELECT 1 AS c1), t2 AS (SELECT 2 AS c2) SELECT t1.*, t2.*, 3 FROM t1, t2",
+            read={
+                "": "WITH t1 AS (SELECT 1 AS c1), t2 AS (SELECT 2 AS c2) SELECT *, 3 FROM t1, t2",
+            },
+        )
+        self.validate_all(
+            'SELECT "A".*, "B".*, 3 FROM "A" JOIN "B" ON 1 = 1',
+            read={
+                "": 'SELECT *, 3 FROM "A" JOIN "B" ON 1=1',
+            },
+        )
+        self.validate_all(
+            "SELECT s.*, q.*, 7 FROM (SELECT 1 AS x) AS s CROSS JOIN (SELECT 2 AS y) AS q",
+            read={
+                "": "SELECT *, 7 FROM (SELECT 1 AS x) s CROSS JOIN (SELECT 2 AS y) q",
+            },
+        )
+
     def test_type_mappings(self):
         self.validate_identity("CAST(x AS BLOB)", "CAST(x AS VARCHAR)")
         self.validate_identity("CAST(x AS LONGBLOB)", "CAST(x AS VARCHAR)")