fix(starrocks): exp.Unnest transpilation

Author: lin.zhang

sqlglot/dialects/starrocks.py

@@ -35,6 +35,12 @@ def _parse_unnest(self, with_alias: bool = True) -> t.Optional[exp.Unnest]:
             if unnest:
                 alias = unnest.args.get("alias")
 
+                if not alias:
+                    # Starrocks defaults to naming the table alias as "unnest"
+                    alias = exp.TableAlias(
+                        this=exp.to_identifier("unnest"), columns=[exp.to_identifier("unnest")]
+                    )
+                    unnest.set("alias", alias)
                 if alias and not alias.args.get("columns"):
                     # Starrocks defaults to naming the UNNEST column as "unnest"
                     # if it's not otherwise specified

tests/dialects/test_starrocks.py

@@ -35,6 +35,29 @@ def test_unnest(self):
             "SELECT student, score, t.unnest FROM tests CROSS JOIN LATERAL UNNEST(scores) AS t",
             "SELECT student, score, t.unnest FROM tests CROSS JOIN LATERAL UNNEST(scores) AS t(unnest)",
         )
+        self.validate_identity(
+            "SELECT student, score, unnest.unnest FROM tests CROSS JOIN LATERAL UNNEST(scores)",
+            "SELECT student, score, unnest.unnest FROM tests CROSS JOIN LATERAL UNNEST(scores) AS unnest(unnest)",
+        )
+        self.validate_all(
+            r"""SELECT * FROM UNNEST(array['John','Jane','Jim','Jamie'], array[24,25,26,27]) AS t(name, age)""",
+            write={
+                "postgres": "SELECT * FROM UNNEST(ARRAY['John', 'Jane', 'Jim', 'Jamie'], ARRAY[24, 25, 26, 27]) AS t(name, age)",
+                "spark": "SELECT * FROM EXPLODE(ARRAY('John', 'Jane', 'Jim', 'Jamie'), ARRAY(24, 25, 26, 27)) AS "
+                "t(name, age)",
+            },
+        )
+        # Use UNNEST to convert into multiple columns
+        # see: https://docs.starrocks.io/docs/sql-reference/sql-functions/array-functions/unnest/
+        self.validate_all(
+            r"""SELECT id, t.type, t.scores FROM example_table, unnest(split(type, ";"), scores) AS t(type,scores)""",
+            write={
+                "postgres": "SELECT id, t.type, t.scores FROM example_table, UNNEST(SPLIT(type, ';'), scores) AS "
+                "t(type, scores)",
+                "spark": "SELECT id, t.type, t.scores FROM example_table LATERAL VIEW EXPLODE(SPLIT(type, CONCAT"
+                r"""('\\Q', ';'))) t AS type LATERAL VIEW EXPLODE(scores) t AS scores""",
+            },
+        )
 
         lateral_explode_sqls = [
             "SELECT id, t.col FROM tbl, UNNEST(scores) AS t(col)",