feat(snowflake): Transpile BQ's ARRAY(SELECT AS STRUCT ...) (#5140)

* feat(snowflake): Transpile ARRAY(SELECT AS STRUCT ...)

* Reuse existing selection

Author: VaggelisD

sqlglot/dialects/snowflake.py

@@ -1017,7 +1017,6 @@ class Generator(generator.Generator):
             exp.ApproxDistinct: rename_func("APPROX_COUNT_DISTINCT"),
             exp.ArgMax: rename_func("MAX_BY"),
             exp.ArgMin: rename_func("MIN_BY"),
-            exp.Array: inline_array_sql,
             exp.ArrayConcat: lambda self, e: self.arrayconcat_sql(e, name="ARRAY_CAT"),
             exp.ArrayContains: lambda self, e: self.func("ARRAY_CONTAINS", e.expression, e.this),
             exp.AtTimeZone: lambda self, e: self.func(
@@ -1427,3 +1426,29 @@ def arrayagg_sql(self, expression: exp.ArrayAgg) -> str:
                 expr_sql = self.sql(exp.WithinGroup(this=expr_sql, expression=order))
 
             return expr_sql
+
+        def array_sql(self, expression: exp.Array) -> str:
+            expressions = expression.expressions
+
+            first_expr = seq_get(expressions, 0)
+            if isinstance(first_expr, exp.Select):
+                # SELECT AS STRUCT foo AS alias_foo -> ARRAY_AGG(OBJECT_CONSTRUCT('alias_foo', foo))
+                if first_expr.text("kind").upper() == "STRUCT":
+                    object_construct_args = []
+                    for expr in first_expr.expressions:
+                        # Alias case: SELECT AS STRUCT foo AS alias_foo -> OBJECT_CONSTRUCT('alias_foo', foo)
+                        # Column case: SELECT AS STRUCT foo -> OBJECT_CONSTRUCT('foo', foo)
+                        name = expr.this if isinstance(expr, exp.Alias) else expr
+
+                        object_construct_args.extend([exp.Literal.string(expr.alias_or_name), name])
+
+                    array_agg = exp.ArrayAgg(
+                        this=_build_object_construct(args=object_construct_args)
+                    )
+
+                    first_expr.set("kind", None)
+                    first_expr.set("expressions", [array_agg])
+
+                    return self.sql(first_expr.subquery())
+
+            return inline_array_sql(self, expression)

tests/dialects/test_bigquery.py

@@ -2583,3 +2583,36 @@ def test_array_agg(self):
                     "snowflake": "SELECT ARRAY_AGG(x) WITHIN GROUP (ORDER BY col1 ASC NULLS FIRST, col2 DESC NULLS LAST)",
                 },
             )
+
+    def test_select_as_struct(self):
+        self.validate_all(
+            "SELECT ARRAY(SELECT AS STRUCT x1 AS x1, x2 AS x2 FROM t) AS array_col",
+            write={
+                "bigquery": "SELECT ARRAY(SELECT AS STRUCT x1 AS x1, x2 AS x2 FROM t) AS array_col",
+                "snowflake": "SELECT (SELECT ARRAY_AGG(OBJECT_CONSTRUCT('x1', x1, 'x2', x2)) FROM t) AS array_col",
+            },
+        )
+
+        self.validate_all(
+            "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT x1 AS alias_x1, x2 /* test */ FROM t2) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+            write={
+                "bigquery": "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT x1 AS alias_x1, x2 /* test */ FROM t2) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+                "snowflake": "WITH t1 AS (SELECT (SELECT ARRAY_AGG(OBJECT_CONSTRUCT('alias_x1', x1, 'x2', x2 /* test */)) FROM t2) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+            },
+        )
+
+        self.validate_all(
+            "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT 1 AS a, 2 AS b) AS array_col) SELECT array_col[0].a, array_col[0].b FROM t1",
+            write={
+                "bigquery": "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT 1 AS a, 2 AS b) AS array_col) SELECT array_col[0].a, array_col[0].b FROM t1",
+                "snowflake": "WITH t1 AS (SELECT (SELECT ARRAY_AGG(OBJECT_CONSTRUCT('a', 1, 'b', 2))) AS array_col) SELECT array_col[0].a, array_col[0].b FROM t1",
+            },
+        )
+
+        self.validate_all(
+            "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT x1 AS alias_x1, x2 /* test */ FROM t2 WHERE x2 = 4) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+            write={
+                "bigquery": "WITH t1 AS (SELECT ARRAY(SELECT AS STRUCT x1 AS alias_x1, x2 /* test */ FROM t2 WHERE x2 = 4) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+                "snowflake": "WITH t1 AS (SELECT (SELECT ARRAY_AGG(OBJECT_CONSTRUCT('alias_x1', x1, 'x2', x2 /* test */)) FROM t2 WHERE x2 = 4) AS array_col) SELECT array_col[0].alias_x1, array_col[0].x2 FROM t1",
+            },
+        )