From 6419ff6fb1ce737367e8e2a43149900a77326325 Mon Sep 17 00:00:00 2001
From: Tanner <tangenta@126.com>
Date: Sun, 29 Sep 2019 00:31:31 +0800
Subject: [PATCH] ddl: allow multiple `unique` attributes in a column (#12165)

---
 ddl/db_integration_test.go | 14 ++++++++++++++
 ddl/ddl_api.go             | 18 ++++++++++++------
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/ddl/db_integration_test.go b/ddl/db_integration_test.go
index 0c259f637fa94..5eda083244dfc 100644
--- a/ddl/db_integration_test.go
+++ b/ddl/db_integration_test.go
@@ -923,3 +923,17 @@ func (s *testIntegrationSuite) TestDropAutoIncrement(c *C) {
 	tk.MustExec("alter table t1 modify column a int")
 	tk.MustExec("set @@tidb_allow_remove_auto_inc = off")
 }
+
+func (s *testIntegrationSuite) TestMultipleUnique(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("create database if not exists test")
+	tk.MustExec("use test")
+
+	tk.MustExec("drop table if exists multi_unique")
+	tk.MustExec("create table multi_unique (a int unique unique)")
+	tk.MustExec("drop table multi_unique")
+	tk.MustExec("create table multi_unique (a int key primary key unique unique)")
+	tk.MustExec("drop table multi_unique")
+	tk.MustExec("create table multi_unique (a int key unique unique key unique)")
+	tk.MustExec("drop table multi_unique")
+}
diff --git a/ddl/ddl_api.go b/ddl/ddl_api.go
index 6c55317e14b44..7b7dedd245b2c 100644
--- a/ddl/ddl_api.go
+++ b/ddl/ddl_api.go
@@ -496,13 +496,19 @@ 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 {