fix(duckdb)!: Fix BQ's exp.Date transpilation (#6595)

Author: VaggelisD

sqlglot/dialects/duckdb.py

@@ -144,17 +144,20 @@ def _to_boolean_sql(self: DuckDB.Generator, expression: exp.ToBoolean) -> str:
 
 # BigQuery -> DuckDB conversion for the DATE function
 def _date_sql(self: DuckDB.Generator, expression: exp.Date) -> str:
-    result = f"CAST({self.sql(expression, 'this')} AS DATE)"
+    this = expression.this
     zone = self.sql(expression, "zone")
 
     if zone:
-        date_str = self.func("STRFTIME", result, "'%d/%m/%Y'")
-        date_str = f"{date_str} || ' ' || {zone}"
-
-        # This will create a TIMESTAMP with time zone information
-        result = self.func("STRPTIME", date_str, "'%d/%m/%Y %Z'")
-
-    return result
+        # BigQuery considers "this" at UTC, converts it to the specified
+        # time zone and then keeps only the DATE part
+        # To micmic that, we:
+        #   (1) Cast to TIMESTAMP to remove DuckDB's local tz
+        #   (2) Apply consecutive AtTimeZone calls for UTC -> zone conversion
+        this = exp.cast(this, exp.DataType.Type.TIMESTAMP)
+        at_utc = exp.AtTimeZone(this=this, zone=exp.Literal.string("UTC"))
+        this = exp.AtTimeZone(this=at_utc, zone=zone)
+
+    return self.sql(exp.cast(expression=this, to=exp.DataType.Type.DATE))
 
 
 # BigQuery -> DuckDB conversion for the TIME_DIFF function

tests/dialects/test_duckdb.py

@@ -1358,11 +1358,17 @@ def test_time(self):
             read={"bigquery": "SELECT DATE(DATETIME '2016-12-25 23:59:59')"},
         )
         self.validate_all(
-            "SELECT STRPTIME(STRFTIME(CAST(CAST('2016-12-25' AS TIMESTAMPTZ) AS DATE), '%d/%m/%Y') || ' ' || 'America/Los_Angeles', '%d/%m/%Y %Z')",
+            "SELECT CAST(CAST(CAST('2016-12-25' AS TIMESTAMPTZ) AS TIMESTAMP) AT TIME ZONE 'UTC' AT TIME ZONE 'America/Los_Angeles' AS DATE)",
             read={
                 "bigquery": "SELECT DATE(TIMESTAMP '2016-12-25', 'America/Los_Angeles')",
             },
         )
+        self.validate_all(
+            "SELECT CAST(CAST('2024-01-15 23:30:00' AS TIMESTAMP) AT TIME ZONE 'UTC' AT TIME ZONE 'Europe/Berlin' AS DATE)",
+            read={
+                "bigquery": "SELECT DATE('2024-01-15 23:30:00', 'Europe/Berlin')",
+            },
+        )
         self.validate_all(
             "SELECT CAST(CAST(STRPTIME('05/06/2020', '%m/%d/%Y') AS DATE) AS DATE)",
             read={"bigquery": "SELECT DATE(PARSE_DATE('%m/%d/%Y', '05/06/2020'))"},