ddl: allow multiple unique attributes in a column

ddl/db_integration_test.go

@@ -1568,6 +1568,18 @@ func (s *testIntegrationSuite3) TestAlterColumn(c *C) {
 	_, err = s.tk.Exec("alter table t1 modify column c bigint;")
 	c.Assert(err, NotNil)
 	c.Assert(err.Error(), Equals, "[ddl:1071]Specified key was too long; max key length is 3072 bytes")
+
+	s.tk.MustExec("drop table if exists multi_unique")
+	s.tk.MustExec("create table multi_unique (a int unique unique)")
+	s.tk.MustExec("drop table multi_unique")
+	s.tk.MustExec("create table multi_unique (a int key primary key unique unique)")
+	s.tk.MustExec("drop table multi_unique")
+	s.tk.MustExec("create table multi_unique (a int key unique unique key unique)")
+	s.tk.MustExec("drop table multi_unique")
+	s.tk.MustExec("create table multi_unique (a serial serial default value)")
+	s.tk.MustExec("drop table multi_unique")
+	s.tk.MustExec("create table multi_unique (a serial serial default value serial default value)")
+	s.tk.MustExec("drop table multi_unique")
 }
 
 func (s *testIntegrationSuite) assertWarningExec(c *C, sql string, expectedWarn *terror.Error) {

ddl/ddl_api.go

@@ -527,13 +527,19 @@ func columnDefToCol(ctx sessionctx.Context, offset int, colDef *ast.ColumnDef, o
 			case ast.ColumnOptionAutoIncrement:
 				col.Flag |= mysql.AutoIncrementFlag
 			case ast.ColumnOptionPrimaryKey:
-				constraint := &ast.Constraint{Tp: ast.ConstraintPrimaryKey, Keys: keys}
-				constraints = append(constraints, constraint)
-				col.Flag |= mysql.PriKeyFlag
+				// Check PriKeyFlag first to avoid extra duplicate constraints.
+				if col.Flag&mysql.PriKeyFlag == 0 {
+					constraint := &ast.Constraint{Tp: ast.ConstraintPrimaryKey, Keys: keys}
+					constraints = append(constraints, constraint)
+					col.Flag |= mysql.PriKeyFlag
+				}
 			case ast.ColumnOptionUniqKey:
-				constraint := &ast.Constraint{Tp: ast.ConstraintUniqKey, Name: colDef.Name.Name.O, Keys: keys}
-				constraints = append(constraints, constraint)
-				col.Flag |= mysql.UniqueKeyFlag
+				// Check UniqueFlag first to avoid extra duplicate constraints.
+				if col.Flag&mysql.UniqueFlag == 0 {
+					constraint := &ast.Constraint{Tp: ast.ConstraintUniqKey, Keys: keys}
+					constraints = append(constraints, constraint)
+					col.Flag |= mysql.UniqueKeyFlag
+				}
 			case ast.ColumnOptionDefaultValue:
 				hasDefaultValue, err = setDefaultValue(ctx, col, v)
 				if err != nil {