Repository: tobymao/sqlglot

Issue:
BigQuery -> Snowflake Translation Error with DATE_SUB 
SQLGlot incorrectly transpiles `DATE_SUB` from BigQuery to Snowflake. This function does not exist in Snowflake, and `DATEADD` must be used instead.

The following snippet:
`sqlglot.transpile("SELECT DATE_SUB(DATE '2008-12-25', INTERVAL 5 DAY)", read="bigquery", write="snowflake", unsupported_level=sqlglot.ErrorLevel.RAISE)[0]`

produces the following output:
`SELECT DATE_SUB(CAST('2008-12-25' AS DATE), '5', DAY)`

The expected output is:
`SELECT DATEADD(DAY, -1, CAST('2008-12-25' AS DATE))`

Hints from issue comments:
@NNhanptnk: Can I pick up this issue ?@VaggelisD: Sure @NNhanptnk, please go for it.@georgesittas: @NNhanptnk any updates on this? If you're already working on it, feel free to take it to the finish line. Otherwise we'll take over and ping you in the PR shortly.

Solution patch:
diff --git a/sqlglot/dialects/dialect.py b/sqlglot/dialects/dialect.py
index 4ed0290a40..58172ef3a6 100644
--- a/sqlglot/dialects/dialect.py
+++ b/sqlglot/dialects/dialect.py
@@ -15,7 +15,13 @@
 from sqlglot.tokens import Token, Tokenizer, TokenType
 from sqlglot.trie import new_trie
 
-DATE_ADD_OR_DIFF = t.Union[exp.DateAdd, exp.TsOrDsAdd, exp.DateDiff, exp.TsOrDsDiff]
+DATE_ADD_OR_DIFF = t.Union[
+    exp.DateAdd,
+    exp.DateDiff,
+    exp.DateSub,
+    exp.TsOrDsAdd,
+    exp.TsOrDsDiff,
+]
 DATE_ADD_OR_SUB = t.Union[exp.DateAdd, exp.TsOrDsAdd, exp.DateSub]
 JSON_EXTRACT_TYPE = t.Union[exp.JSONExtract, exp.JSONExtractScalar]
 
diff --git a/sqlglot/dialects/snowflake.py b/sqlglot/dialects/snowflake.py
index 92a1671a3e..063f472435 100644
--- a/sqlglot/dialects/snowflake.py
+++ b/sqlglot/dialects/snowflake.py
@@ -1097,7 +1097,11 @@ def unnest_sql(self, expression: exp.Unnest) -> str:
             else:
                 unnest_alias = exp.TableAlias(this="_u", columns=columns)
 
-            explode = f"TABLE(FLATTEN(INPUT => {self.sql(expression.expressions[0])}))"
+            table_input = self.sql(expression.expressions[0])
+            if not table_input.startswith("INPUT =>"):
+                table_input = f"INPUT => {table_input}"
+
+            explode = f"TABLE(FLATTEN({table_input}))"
             alias = self.sql(unnest_alias)
             alias = f" AS {alias}" if alias else ""
             return f"{explode}{alias}"
@@ -1211,3 +1215,12 @@ def timetostr_sql(self, expression: exp.TimeToStr) -> str:
                 this = exp.cast(this, exp.DataType.Type.TIMESTAMP)
 
             return self.func("TO_CHAR", this, self.format_time(expression))
+
+        def datesub_sql(self, expression: exp.DateSub) -> str:
+            value = expression.expression
+            if value:
+                value.replace(value * (-1))
+            else:
+                self.unsupported("DateSub cannot be transpiled if the subtracted count is unknown")
+
+            return date_delta_sql("DATEADD")(self, expression)


Test patch:
diff --git a/tests/dialects/test_bigquery.py b/tests/dialects/test_bigquery.py
index ec16dba243..dbe4401af6 100644
--- a/tests/dialects/test_bigquery.py
+++ b/tests/dialects/test_bigquery.py
@@ -315,6 +315,14 @@ def test_bigquery(self):
             "SELECT CAST(1 AS INT64)",
         )
 
+        self.validate_all(
+            "SELECT DATE_SUB(DATE '2008-12-25', INTERVAL 5 DAY)",
+            write={
+                "bigquery": "SELECT DATE_SUB(CAST('2008-12-25' AS DATE), INTERVAL '5' DAY)",
+                "duckdb": "SELECT CAST('2008-12-25' AS DATE) - INTERVAL '5' DAY",
+                "snowflake": "SELECT DATEADD(DAY, '5' * -1, CAST('2008-12-25' AS DATE))",
+            },
+        )
         self.validate_all(
             "EDIT_DISTANCE(col1, col2, max_distance => 3)",
             write={
diff --git a/tests/dialects/test_snowflake.py b/tests/dialects/test_snowflake.py
index 5164b8215f..1d55f35d67 100644
--- a/tests/dialects/test_snowflake.py
+++ b/tests/dialects/test_snowflake.py
@@ -21,27 +21,6 @@ def test_snowflake(self):
         expr.selects[0].assert_is(exp.AggFunc)
         self.assertEqual(expr.sql(dialect="snowflake"), "SELECT APPROX_TOP_K(C4, 3, 5) FROM t")
 
-        self.assertEqual(
-            exp.select(exp.Explode(this=exp.column("x")).as_("y", quoted=True)).sql(
-                "snowflake", pretty=True
-            ),
-            """SELECT
-  IFF(_u.pos = _u_2.pos_2, _u_2."y", NULL) AS "y"
-FROM TABLE(FLATTEN(INPUT => ARRAY_GENERATE_RANGE(0, (
-  GREATEST(ARRAY_SIZE(x)) - 1
-) + 1))) AS _u(seq, key, path, index, pos, this)
-CROSS JOIN TABLE(FLATTEN(INPUT => x)) AS _u_2(seq, key, path, pos_2, "y", this)
-WHERE
-  _u.pos = _u_2.pos_2
-  OR (
-    _u.pos > (
-      ARRAY_SIZE(x) - 1
-    ) AND _u_2.pos_2 = (
-      ARRAY_SIZE(x) - 1
-    )
-  )""",
-        )
-
         self.validate_identity("exclude := [foo]")
         self.validate_identity("SELECT CAST([1, 2, 3] AS VECTOR(FLOAT, 3))")
         self.validate_identity("SELECT CONNECT_BY_ROOT test AS test_column_alias")
@@ -1603,6 +1582,27 @@ def test_table_literal(self):
         )
 
     def test_flatten(self):
+        self.assertEqual(
+            exp.select(exp.Explode(this=exp.column("x")).as_("y", quoted=True)).sql(
+                "snowflake", pretty=True
+            ),
+            """SELECT
+  IFF(_u.pos = _u_2.pos_2, _u_2."y", NULL) AS "y"
+FROM TABLE(FLATTEN(INPUT => ARRAY_GENERATE_RANGE(0, (
+  GREATEST(ARRAY_SIZE(x)) - 1
+) + 1))) AS _u(seq, key, path, index, pos, this)
+CROSS JOIN TABLE(FLATTEN(INPUT => x)) AS _u_2(seq, key, path, pos_2, "y", this)
+WHERE
+  _u.pos = _u_2.pos_2
+  OR (
+    _u.pos > (
+      ARRAY_SIZE(x) - 1
+    ) AND _u_2.pos_2 = (
+      ARRAY_SIZE(x) - 1
+    )
+  )""",
+        )
+
         self.validate_all(
             """
             select
@@ -1627,6 +1627,75 @@ def test_flatten(self):
             },
             pretty=True,
         )
+        self.validate_all(
+            """
+            SELECT
+              uc.user_id,
+              uc.start_ts AS ts,
+              CASE
+                WHEN uc.start_ts::DATE >= '2023-01-01' AND uc.country_code IN ('US') AND uc.user_id NOT IN (
+                  SELECT DISTINCT
+                    _id
+                  FROM
+                    users,
+                    LATERAL FLATTEN(INPUT => PARSE_JSON(flags)) datasource
+                  WHERE datasource.value:name = 'something'
+                )
+                  THEN 'Sample1'
+                  ELSE 'Sample2'
+              END AS entity
+            FROM user_countries AS uc
+            LEFT JOIN (
+              SELECT user_id, MAX(IFF(service_entity IS NULL,1,0)) AS le_null
+              FROM accepted_user_agreements
+              GROUP BY 1
+            ) AS aua
+              ON uc.user_id = aua.user_id
+            """,
+            write={
+                "snowflake": """SELECT
+  uc.user_id,
+  uc.start_ts AS ts,
+  CASE
+    WHEN CAST(uc.start_ts AS DATE) >= '2023-01-01'
+    AND uc.country_code IN ('US')
+    AND uc.user_id <> ALL (
+      SELECT DISTINCT
+        _id
+      FROM users, LATERAL IFF(_u.pos = _u_2.pos_2, _u_2.entity, NULL) AS datasource(SEQ, KEY, PATH, INDEX, VALUE, THIS)
+      WHERE
+        GET_PATH(datasource.value, 'name') = 'something'
+    )
+    THEN 'Sample1'
+    ELSE 'Sample2'
+  END AS entity
+FROM user_countries AS uc
+LEFT JOIN (
+  SELECT
+    user_id,
+    MAX(IFF(service_entity IS NULL, 1, 0)) AS le_null
+  FROM accepted_user_agreements
+  GROUP BY
+    1
+) AS aua
+  ON uc.user_id = aua.user_id
+CROSS JOIN TABLE(FLATTEN(INPUT => ARRAY_GENERATE_RANGE(0, (
+  GREATEST(ARRAY_SIZE(INPUT => PARSE_JSON(flags))) - 1
+) + 1))) AS _u(seq, key, path, index, pos, this)
+CROSS JOIN TABLE(FLATTEN(INPUT => PARSE_JSON(flags))) AS _u_2(seq, key, path, pos_2, entity, this)
+WHERE
+  _u.pos = _u_2.pos_2
+  OR (
+    _u.pos > (
+      ARRAY_SIZE(INPUT => PARSE_JSON(flags)) - 1
+    )
+    AND _u_2.pos_2 = (
+      ARRAY_SIZE(INPUT => PARSE_JSON(flags)) - 1
+    )
+  )""",
+            },
+            pretty=True,
+        )
 
         # All examples from https://docs.snowflake.com/en/sql-reference/functions/flatten.html#syntax
         self.validate_all(