feat(snowflake)!: update transpilation of DATE_TRUNC to duckdb

sqlglot/dialects/duckdb.py

@@ -2451,6 +2451,21 @@ def hexstring_sql(
 
             return self.sql(to_hex)
 
+        def datetrunc_sql(self, expression: exp.DateTrunc) -> str:
+            unit = unit_to_str(expression)
+            date = expression.this
+            result = self.func("DATE_TRUNC", unit, date)
+
+            if expression.args.get("input_type_preserved"):
+                if not date.type:
+                    from sqlglot.optimizer.annotate_types import annotate_types
+
+                    date = annotate_types(date, dialect=self.dialect)
+
+                if date.type and date.is_type(*exp.DataType.TEMPORAL_TYPES):
+                    return self.sql(exp.Cast(this=result, to=date.type))
+            return result
+
         def timestamptrunc_sql(self, expression: exp.TimestampTrunc) -> str:
             unit = unit_to_str(expression)
             zone = expression.args.get("zone")
@@ -2465,7 +2480,27 @@ def timestamptrunc_sql(self, expression: exp.TimestampTrunc) -> str:
                 result_sql = self.func("DATE_TRUNC", unit, timestamp)
                 return self.sql(exp.AtTimeZone(this=result_sql, zone=zone))
 
-            return self.func("DATE_TRUNC", unit, timestamp)
+            result = self.func("DATE_TRUNC", unit, timestamp)
+            if expression.args.get("input_type_preserved"):
+                if not timestamp.type:
+                    from sqlglot.optimizer.annotate_types import annotate_types
+
+                    timestamp = annotate_types(timestamp, dialect=self.dialect)
+
+                if timestamp.type and timestamp.is_type(
+                    exp.DataType.Type.TIME, exp.DataType.Type.TIMETZ
+                ):
+                    dummy_date = exp.Cast(
+                        this=exp.Literal.string("1970-01-01"),
+                        to=exp.DataType(this=exp.DataType.Type.DATE),
+                    )
+                    date_time = exp.Add(this=dummy_date, expression=timestamp)
+                    result = self.func("DATE_TRUNC", unit, date_time)
+                    return self.sql(exp.Cast(this=result, to=timestamp.type))
+
+                if timestamp.type and timestamp.is_type(*exp.DataType.TEMPORAL_TYPES):
+                    return self.sql(exp.Cast(this=result, to=timestamp.type))
+            return result
 
         def trim_sql(self, expression: exp.Trim) -> str:
             expression.this.replace(_cast_to_varchar(expression.this))

sqlglot/dialects/snowflake.py

@@ -32,7 +32,7 @@
     groupconcat_sql,
 )
 from sqlglot.generator import unsupported_args
-from sqlglot.helper import find_new_name, flatten, is_int, seq_get
+from sqlglot.helper import find_new_name, flatten, is_date_unit, is_int, seq_get
 from sqlglot.optimizer.scope import build_scope, find_all_in_scope
 from sqlglot.tokens import TokenType
 from sqlglot.typing.snowflake import EXPRESSION_METADATA
@@ -259,7 +259,13 @@ def _parse(self: Snowflake.Parser) -> exp.Show:
 
 def _date_trunc_to_time(args: t.List) -> exp.DateTrunc | exp.TimestampTrunc:
     trunc = date_trunc_to_time(args)
-    trunc.set("unit", map_date_part(trunc.args["unit"]))
+    unit = map_date_part(trunc.args["unit"])
+    trunc.set("unit", unit)
+    is_time_input = trunc.this.is_type(exp.DataType.Type.TIME, exp.DataType.Type.TIMETZ)
+    if (isinstance(trunc, exp.TimestampTrunc) and is_date_unit(unit) or is_time_input) or (
+        isinstance(trunc, exp.DateTrunc) and not is_date_unit(unit)
+    ):
+        trunc.set("input_type_preserved", True)
     return trunc
 
 

sqlglot/expressions.py

@@ -6509,7 +6509,7 @@ class DateDiff(Func, TimeUnit):
 
 
 class DateTrunc(Func):
-    arg_types = {"unit": True, "this": True, "zone": False}
+    arg_types = {"unit": True, "this": True, "zone": False, "input_type_preserved": False}
 
     def __init__(self, **args):
         # Across most dialects it's safe to unabbreviate the unit (e.g. 'Q' -> 'QUARTER') except Oracle
@@ -6669,7 +6669,7 @@ class TimestampDiff(Func, TimeUnit):
 
 
 class TimestampTrunc(Func, TimeUnit):
-    arg_types = {"this": True, "unit": True, "zone": False}
+    arg_types = {"this": True, "unit": True, "zone": False, "input_type_preserved": False}
 
 
 class TimeSlice(Func, TimeUnit):

tests/dialects/test_snowflake.py

@@ -2668,7 +2668,56 @@ def test_timestamps(self):
         self.validate_identity("DATEADD(y, 5, x)", "DATEADD(YEAR, 5, x)")
         self.validate_identity("DATE_PART(yyy, x)", "DATE_PART(YEAR, x)")
         self.validate_identity("DATE_TRUNC(yr, x)", "DATE_TRUNC('YEAR', x)")
+        self.validate_all(
+            "DATE_TRUNC('YEAR', CAST('2024-06-15' AS DATE))",
+            write={
+                "snowflake": "DATE_TRUNC('YEAR', CAST('2024-06-15' AS DATE))",
+                "duckdb": "DATE_TRUNC('YEAR', CAST('2024-06-15' AS DATE))",
+            },
+        )
+        self.validate_all(
+            "DATE_TRUNC('HOUR', CAST('2026-01-01 00:00:00' AS TIMESTAMP))",
+            write={
+                "snowflake": "DATE_TRUNC('HOUR', CAST('2026-01-01 00:00:00' AS TIMESTAMP))",
+                "duckdb": "DATE_TRUNC('HOUR', CAST('2026-01-01 00:00:00' AS TIMESTAMP))",
+            },
+        )
+        # Snowflake's DATE_TRUNC return type matches type of the expresison
+        # DuckDB's DATE_TRUNC return type matches type of granularity part.
+        # In Snowflake --> DuckDB, DATE_TRUNC(date_part, timestamp) should be cast to timestamp to preserve Snowflake behavior.
+        self.validate_all(
+            "DATE_TRUNC(YEAR, TIMESTAMP '2026-01-01 00:00:00')",
+            write={
+                "snowflake": "DATE_TRUNC('YEAR', CAST('2026-01-01 00:00:00' AS TIMESTAMP))",
+                "duckdb": "CAST(DATE_TRUNC('YEAR', CAST('2026-01-01 00:00:00' AS TIMESTAMP)) AS TIMESTAMP)",
+            },
+        )
+        self.validate_all(
+            "DATE_TRUNC(MONTH, CAST('2024-06-15 14:23:45' AS TIMESTAMPTZ))",
+            write={
+                "snowflake": "DATE_TRUNC('MONTH', CAST('2024-06-15 14:23:45' AS TIMESTAMPTZ))",
+                "duckdb": "CAST(DATE_TRUNC('MONTH', CAST('2024-06-15 14:23:45' AS TIMESTAMPTZ)) AS TIMESTAMPTZ)",
+            },
+        )
+
+        # In Snowflake --> DuckDB, DATE_TRUNC(time_part, date) should be cast to date to preserve Snowflake behavior.
+        self.validate_all(
+            "DATE_TRUNC('HOUR', CAST('2026-01-01' AS DATE))",
+            write={
+                "snowflake": "DATE_TRUNC('HOUR', CAST('2026-01-01' AS DATE))",
+                "duckdb": "CAST(DATE_TRUNC('HOUR', CAST('2026-01-01' AS DATE)) AS DATE)",
+            },
+        )
 
+        # DuckDB does not support DATE_TRUNC(time_part, time), so we add a dummy date to generate DATE_TRUNC(time_part, date) --> DATE in DuckDB
+        # Then it is casted to a time (HH:MM:SS) to match Snowflake.
+        self.validate_all(
+            "DATE_TRUNC('HOUR', CAST('14:23:45.123456' AS TIME))",
+            write={
+                "snowflake": "DATE_TRUNC('HOUR', CAST('14:23:45.123456' AS TIME))",
+                "duckdb": "CAST(DATE_TRUNC('HOUR', CAST('1970-01-01' AS DATE) + CAST('14:23:45.123456' AS TIME)) AS TIME)",
+            },
+        )
         self.validate_identity("TO_DATE('12345')").assert_is(exp.Anonymous)
 
         self.validate_identity(