feat(expressions): add NULLIF helper

expressions.go

@@ -133,6 +133,14 @@ func COALESCE(vals ...interface{}) exp.SQLFunctionExpression {
 	return Func("COALESCE", vals...)
 }
 
+// Creates a new NULLIF sql function
+//
+//	NULLIF(I("a"), "a") -> NULLIF("a", 'a')
+//	NULLIF("a", "a") -> NULLIF("a", 'a')
+func NULLIF(column interface{}, value interface{}) exp.SQLFunctionExpression {
+	return Func("NULLIF", column, value)
+}
+
 //nolint:stylecheck,revive // sql function name
 func ROW_NUMBER() exp.SQLFunctionExpression {
 	return Func("ROW_NUMBER")

expressions_example_test.go

@@ -937,6 +937,21 @@ func ExampleMIN_havingClause() {
 	// SELECT MIN("a") AS "MIN" FROM "test" GROUP BY "a" HAVING (MIN("a") > ?) [10]
 }
 
+func ExampleNULLIF() {
+	ds := goqu.From("test").Select(
+		goqu.NULLIF(goqu.C("a"), "a"),
+		goqu.NULLIF(goqu.C("a"), goqu.C("b")),
+	)
+	sql, args, _ := ds.ToSQL()
+	fmt.Println(sql, args)
+
+	sql, args, _ = ds.Prepared(true).ToSQL()
+	fmt.Println(sql, args)
+	// Output:
+	// SELECT NULLIF("a", 'a'), NULLIF("a", "b") FROM "test" []
+	// SELECT NULLIF("a", ?), NULLIF("a", "b") FROM "test" [a]
+}
+
 func ExampleOn() {
 	ds := goqu.From("test").Join(
 		goqu.T("my_table"),

expressions_test.go

@@ -78,6 +78,10 @@ func (ges *goquExpressionsSuite) TestCOALESCE() {
 	ges.Equal(exp.NewSQLFunctionExpression("COALESCE", goqu.I("col"), nil), goqu.COALESCE(goqu.I("col"), nil))
 }
 
+func (ges *goquExpressionsSuite) TestNULLIF() {
+	ges.Equal(exp.NewSQLFunctionExpression("NULLIF", goqu.I("col"), "test"), goqu.NULLIF(goqu.I("col"), "test"))
+}
+
 func (ges *goquExpressionsSuite) TestROW_NUMBER() {
 	ges.Equal(exp.NewSQLFunctionExpression("ROW_NUMBER"), goqu.ROW_NUMBER())
 }