support DISTINCT

select.go

@@ -123,6 +123,11 @@ func (sb *SelectBuilder) String() string {
 func (sb *SelectBuilder) Build() (sql string, args []interface{}) {
 	buf := &bytes.Buffer{}
 	buf.WriteString("SELECT ")
+
+	if sb.distinct {
+		buf.WriteString("DISTINCT ")
+	}
+
 	buf.WriteString(strings.Join(sb.selectCols, ", "))
 	buf.WriteString(" FROM ")
 	buf.WriteString(strings.Join(sb.tables, ", "))

select_test.go

@@ -29,6 +29,6 @@ func ExampleSelectBuilder() {
 	fmt.Println(args)
 
 	// Output:
-	// SELECT id, name, COUNT(*) AS t FROM demo.user WHERE id > ? AND name LIKE ? AND (id_card IS NULL OR status IN (?, ?, ?)) AND modified_at > created_at + ? GROUP BY status HAVING status NOT IN (?, ?) ORDER BY modified_at ASC LIMIT 10 OFFSET 5
+	// SELECT DISTINCT id, name, COUNT(*) AS t FROM demo.user WHERE id > ? AND name LIKE ? AND (id_card IS NULL OR status IN (?, ?, ?)) AND modified_at > created_at + ? GROUP BY status HAVING status NOT IN (?, ?) ORDER BY modified_at ASC LIMIT 10 OFFSET 5
 	// [1234 %Du 1 2 5 86400 4 5]
 }