Remove duplicate options before building SQL

insert.go

@@ -78,8 +78,16 @@ func (d *insertData) ToSql() (sqlStr string, args []interface{}, err error) {
 		sql.WriteString(" ")
 	}
 
-	if len(d.Options) > 0 {
-		sql.WriteString(strings.Join(d.Options, " "))
+	options := make([]string, 0)
+	optionsMap := make(map[string]bool)
+	for _, opt := range d.Options {
+		if _, ok := optionsMap[opt]; !ok {
+			options = append(options, opt)
+			optionsMap[opt] = true
+		}
+	}
+	if len(options) > 0 {
+		sql.WriteString(strings.Join(options, " "))
 		sql.WriteString(" ")
 	}
 

insert_test.go

@@ -101,3 +101,28 @@ func TestInsertBuilderReplace(t *testing.T) {
 
 	assert.Equal(t, expectedSQL, sql)
 }
+
+func TestInsertBuilderDuplicateOptions(t *testing.T) {
+	b := Insert("").
+		Prefix("WITH prefix AS ?", 0).
+		Into("a").
+		Options("DELAYED", "DELAYED", "IGNORE").
+		Columns("b", "c").
+		Values(1, 2).
+		Values(3, Expr("? + 1", 4)).
+		OnConflict("DO NOTHING").
+		Returning("d", "e")
+
+	sql, args, err := b.ToSql()
+	assert.NoError(t, err)
+
+	expectedSQL :=
+		"WITH prefix AS ? " +
+			"INSERT DELAYED IGNORE INTO a (b,c) VALUES (?,?),(?,? + 1) " +
+			"ON CONFLICT DO NOTHING " +
+			"RETURNING d, e"
+	assert.Equal(t, expectedSQL, sql)
+
+	expectedArgs := []interface{}{0, 1, 2, 3, 4}
+	assert.Equal(t, expectedArgs, args)
+}

select.go

@@ -84,8 +84,16 @@ func (d *selectData) toSql() (sqlStr string, args []interface{}, err error) {
 
 	sql.WriteString("SELECT ")
 
-	if len(d.Options) > 0 {
-		sql.WriteString(strings.Join(d.Options, " "))
+	options := make([]string, 0)
+	optionsMap := make(map[string]bool)
+	for _, opt := range d.Options {
+		if _, ok := optionsMap[opt]; !ok {
+			options = append(options, opt)
+			optionsMap[opt] = true
+		}
+	}
+	if len(options) > 0 {
+		sql.WriteString(strings.Join(options, " "))
 		sql.WriteString(" ")
 	}
 

select_test.go

@@ -249,6 +249,20 @@ func TestSelectWithEmptyStringWhereClause(t *testing.T) {
 	assert.Equal(t, "SELECT * FROM users", sql)
 }
 
+func TestSelectBuilderDuplicateDistinct(t *testing.T) {
+	sql, _, err := Select("a", "b").
+		Distinct().
+		Distinct().
+		Columns("c").
+		From("e").
+		ToSql()
+
+	assert.NoError(t, err)
+
+	expectedSql := "SELECT DISTINCT a, b, c FROM e"
+	assert.Equal(t, expectedSql, sql)
+}
+
 func ExampleSelect() {
 	Select("id", "created", "first_name").From("users") // ... continue building up your query