Fix Select with specific symbol, close #3157

chainable_api.go

@@ -60,11 +60,11 @@ func (db *DB) Table(name string) (tx *DB) {
 
 // Distinct specify distinct fields that you want querying
 func (db *DB) Distinct(args ...interface{}) (tx *DB) {
-	tx = db
+	tx = db.getInstance()
+	tx.Statement.Distinct = true
 	if len(args) > 0 {
 		tx = tx.Select(args[0], args[1:]...)
 	}
-	tx.Statement.Distinct = true
 	return tx
 }
 
@@ -102,6 +102,7 @@ func (db *DB) Select(query interface{}, args ...interface{}) (tx *DB) {
 					tx.Statement.Selects = append(tx.Statement.Selects, arg...)
 				default:
 					tx.Statement.AddClause(clause.Select{
+						Distinct:   db.Statement.Distinct,
 						Expression: clause.Expr{SQL: v, Vars: args},
 					})
 					return
@@ -109,6 +110,7 @@ func (db *DB) Select(query interface{}, args ...interface{}) (tx *DB) {
 			}
 		} else {
 			tx.Statement.AddClause(clause.Select{
+				Distinct:   db.Statement.Distinct,
 				Expression: clause.Expr{SQL: v, Vars: args},
 			})
 		}

clause/select.go

@@ -30,6 +30,14 @@ func (s Select) Build(builder Builder) {
 
 func (s Select) MergeClause(clause *Clause) {
 	if s.Expression != nil {
+		if s.Distinct {
+			if expr, ok := s.Expression.(Expr); ok {
+				expr.SQL = "DISTINCT " + expr.SQL
+				clause.Expression = expr
+				return
+			}
+		}
+
 		clause.Expression = s.Expression
 	} else {
 		clause.Expression = s

tests/distinct_test.go

@@ -1,8 +1,10 @@
 package tests_test
 
 import (
+	"regexp"
 	"testing"
 
+	"gorm.io/gorm"
 	. "gorm.io/gorm/utils/tests"
 )
 
@@ -57,4 +59,10 @@ func TestDistinct(t *testing.T) {
 	if err := DB.Model(&User{}).Distinct("name").Where("name like ?", "distinct%").Count(&count).Error; err != nil || count != 3 {
 		t.Errorf("failed to query users count, got error: %v, count %v", err, count)
 	}
+
+	dryDB := DB.Session(&gorm.Session{DryRun: true})
+	r := dryDB.Distinct("u.id, u.*").Table("user_speaks as s").Joins("inner join users as u on u.id = s.user_id").Where("s.language_code ='US' or s.language_code ='ES'").Find(&User{})
+	if !regexp.MustCompile(`SELECT DISTINCT u\.id, u\.\* FROM user_speaks as s inner join users as u`).MatchString(r.Statement.SQL.String()) {
+		t.Fatalf("Build Distinct with u.*, but got %v", r.Statement.SQL.String())
+	}
 }