Implement date trunc

dbt/include/sqlite/macros/utils/date_trunc.sql

@@ -0,0 +1,64 @@
+{% macro sqlite__date_trunc(datepart, date) -%}
+{#- Truncate a date to a specified datepart.
+
+`sqlite__date_trunc` always returns a datetime.
+
+Only supports the following date parts:
+"year", "quarter", "month", "week", "day", "hour", "minute", "second"
+
+Makes use of official datetime modifiers when possible.
+For details of date and time functions in sqlite, refer to the official documentation:
+https://www.sqlite.org/lang_datefunc.html -#}
+{#- datepart can be quoted or unquoted, lower or uppercase -#}
+{%- set datepart = datepart.lower().strip("'") -%}
+
+{#- use the official modifier whenever possible -#}
+{%- if datepart == "year" -%} datetime({{ date }}, 'start of year')
+{%- elif datepart == "month" -%} datetime({{ date }}, 'start of month')
+{%- elif datepart == "day" -%} datetime({{ date }}, 'start of day')
+
+{%- elif datepart == "quarter" -%}
+{#- truncate to start of year, then add necessary number of months -#}
+{#- note that we make use of integer division to round down -#}
+datetime(
+    {{ date }},
+    'start of year',
+    '+' || cast((strftime('%m', {{ date }}) - 1) / 3 * 3 as text) || " month"
+)
+
+{%- elif datepart == "week" -%}
+{#- remove {day_no} days and truncate to start of day -#}
+{#- note that week starts at Sunday, i.e. Sunday=0 -#}
+datetime({{ date }}, ('-' || strftime('%w', {{ date }}) || ' day'), 'start of day')
+
+{%- elif datepart == "hour" -%}
+{#- truncate to start of day, then add back hours -#}
+datetime({{ date }}, 'start of day', '+' || strftime('%H', {{ date }}) || " hour")
+
+{%- elif datepart == "minute" -%}
+{#- truncate to start of day, then add back hours and minutes -#}
+datetime(
+    {{ date }},
+    'start of day',
+    '+' || strftime('%H', {{ date }}) || " hour",
+    '+' || strftime('%M', {{ date }}) || " minute"
+)
+{%- elif datepart == "second" -%}
+{#- truncate to start of day, then add back hours, minutes, seconds -#}
+datetime(
+    {{ date }},
+    'start of day',
+    '+' || strftime('%H', {{ date }}) || " hour",
+    '+' || strftime('%M', {{ date }}) || " minute",
+    '+' || strftime('%S', {{ date }}) || " second"
+)
+
+{%- else -%}
+{#- arithmetics for micro-/nanoseconds is more complicated, skipped for now -#}
+{{
+    exceptions.raise_compiler_error(
+        "Unsupported datepart for macro date_trunc in sqlite: {!r}".format(datepart)
+    )
+}}
+{%- endif -%}
+{%- endmacro %}

tests/functional/adapter/utils/test_utils.py

@@ -1,5 +1,6 @@
 import pytest
 from dbt.tests.adapter.utils.base_utils import BaseUtils
+from dbt.tests.adapter.utils.fixture_date_trunc import models__test_date_trunc_yml
 from dbt.tests.adapter.utils.fixture_datediff import (
     seeds__data_datediff_csv,
     models__test_datediff_yml,
@@ -14,7 +15,6 @@
 from dbt.tests.adapter.utils.test_current_timestamp import BaseCurrentTimestampNaive
 from dbt.tests.adapter.utils.test_dateadd import BaseDateAdd
 #from dbt.tests.adapter.utils.test_datediff import BaseDateDiff
-from dbt.tests.adapter.utils.test_date_trunc import BaseDateTrunc
 from dbt.tests.adapter.utils.test_escape_single_quotes import BaseEscapeSingleQuotesQuote
 from dbt.tests.adapter.utils.test_escape_single_quotes import BaseEscapeSingleQuotesBackslash
 from dbt.tests.adapter.utils.test_except import BaseExcept
@@ -129,9 +129,50 @@ class TestDateDiff(BaseDateDiff):
     pass
 
 
-@pytest.mark.skip("TODO: implement date_trunc")
-class TestDateTrunc(BaseDateTrunc):
-    pass
+class TestDateTrunc(BaseUtils):
+    seeds__data_date_trunc_csv = """date_to_trunc,year,quarter,month,week,day,hour,minute,second
+1999-12-31 23:59:59.999999,1999-01-01 00:00:00,1999-10-01 00:00:00,1999-12-01 00:00:00,1999-12-26 00:00:00,1999-12-31 00:00:00,1999-12-31 23:00:00,1999-12-31 23:59:00,1999-12-31 23:59:59
+1999-12-31,1999-01-01 00:00:00,1999-10-01 00:00:00,1999-12-01 00:00:00,1999-12-26 00:00:00,1999-12-31 00:00:00,1999-12-31 00:00:00,1999-12-31 00:00:00,1999-12-31 00:00:00
+1999-01-01,1999-01-01 00:00:00,1999-01-01 00:00:00,1999-01-01 00:00:00,1998-12-27 00:00:00,1999-01-01 00:00:00,1999-01-01 00:00:00,1999-01-01 00:00:00,1999-01-01 00:00:00
+1999-05-16 12:21,1999-01-01 00:00:00,1999-04-01 00:00:00,1999-05-01 00:00:00,1999-05-16 00:00:00,1999-05-16 00:00:00,1999-05-16 12:00:00,1999-05-16 12:21:00,1999-05-16 12:21:00
+"""
+
+    models__test_date_trunc_sql = """
+    with data as (
+        select * from {{ ref('data_date_trunc') }}
+    )
+    """ + " union all ".join(
+        """
+    select
+        {{{{ date_trunc("{datepart}", "date_to_trunc") }}}} as actual,
+        {datepart} as expected
+    from data""".format(
+            datepart=datepart
+        )
+        for datepart in [
+            "year",
+            "quarter",
+            "month",
+            "week",
+            "day",
+            "hour",
+            "minute",
+            "second",
+        ]
+    )
+
+    @pytest.fixture(scope="class")
+    def seeds(self):
+        return {"data_date_trunc.csv": self.seeds__data_date_trunc_csv}
+
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "test_date_trunc.yml": models__test_date_trunc_yml,
+            "test_date_trunc.sql": self.interpolate_macro_namespace(
+                self.models__test_date_trunc_sql, "date_trunc"
+            ),
+        }
 
 
 class TestEscapeSingleQuotes(BaseEscapeSingleQuotesQuote):