From b25b2aa2133276497c923cf003b72eae092a93d5 Mon Sep 17 00:00:00 2001
From: Branislav Lazic <brano2411@hotmail.com>
Date: Fri, 20 Sep 2024 09:47:40 +0200
Subject: [PATCH] Add Postgres DATE_TRUNC function

---
 postgres/functions.go      |  9 +++++++++
 postgres/functions_test.go | 13 ++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/postgres/functions.go b/postgres/functions.go
index 7b6d1e1..75a6925 100644
--- a/postgres/functions.go
+++ b/postgres/functions.go
@@ -332,6 +332,15 @@ var LOCALTIMESTAMP = jet.LOCALTIMESTAMP
 // NOW returns current date and time
 var NOW = jet.NOW
 
+// DATE_TRUNC returns the truncated date and time using optional time zone
+func DATE_TRUNC(field unit, source Expression, timezone ...string) TimestampExpression {
+	if len(timezone) > 0 {
+		return jet.NewTimestampFunc("DATE_TRUNC", jet.FixedLiteral(unitToString(field)), source, jet.FixedLiteral(timezone[0]))
+	}
+
+	return jet.NewTimestampFunc("DATE_TRUNC", jet.FixedLiteral(unitToString(field)), source)
+}
+
 // --------------- Conditional Expressions Functions -------------//
 
 // COALESCE function returns the first of its arguments that is not null.
diff --git a/postgres/functions_test.go b/postgres/functions_test.go
index 4190f70..d0081b0 100644
--- a/postgres/functions_test.go
+++ b/postgres/functions_test.go
@@ -1,6 +1,8 @@
 package postgres
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestROW(t *testing.T) {
 	assertSerialize(t, ROW(SELECT(Int(1))), `ROW((
@@ -10,3 +12,12 @@ func TestROW(t *testing.T) {
      SELECT $2
 ), $3)`)
 }
+
+func TestDATE_TRUNC(t *testing.T) {
+	assertSerialize(t, DATE_TRUNC(YEAR, NOW()), "DATE_TRUNC('YEAR', NOW())")
+	assertSerialize(
+		t,
+		DATE_TRUNC(DAY, NOW().ADD(INTERVAL(1, HOUR)), "Australia/Sydney"),
+		"DATE_TRUNC('DAY', NOW() + INTERVAL '1 HOUR', 'Australia/Sydney')",
+	)
+}