*: support IF EXISTS/IF NOT EXISTS for some DDLs

ddl/db_change_test.go

@@ -888,6 +888,51 @@ func (s *testStateChangeSuite) TestCreateDBIfNotExists(c *C) {
 	s.testParallelExecSQL(c, "create database if not exists test_not_exists;")
 }
 
+// TestDDLIfNotExists parallel exec some DDLs with `if not exists` clause. No error returns is expected.
+func (s *testStateChangeSuite) TestDDLIfNotExists(c *C) {
+	defer s.se.Execute(context.Background(), "drop table test_not_exists")
+	_, err := s.se.Execute(context.Background(), "create table if not exists test_not_exists(a int)")
+	c.Assert(err, IsNil)
+
+	// ADD COLUMN
+	s.testParallelExecSQL(c, "alter table test_not_exists add column if not exists b int")
+
+	// ADD INDEX
+	s.testParallelExecSQL(c, "alter table test_not_exists add index if not exists idx_b (b)")
+
+	// CREATE INDEX
+	s.testParallelExecSQL(c, "create index if not exists idx_b on test_not_exists (b)")
+}
+
+// TestDDLIfExists parallel exec some DDLs with `if exists` clause. No error returns is expected.
+func (s *testStateChangeSuite) TestDDLIfExists(c *C) {
+	defer func() {
+		s.se.Execute(context.Background(), "drop table test_exists")
+		s.se.Execute(context.Background(), "drop table test_exists_2")
+	}()
+	_, err := s.se.Execute(context.Background(), "create table if not exists test_exists (a int key, b int)")
+	c.Assert(err, IsNil)
+
+	// DROP COLUMN
+	s.testParallelExecSQL(c, "alter table test_exists drop column if exists b") // only `a` exists now
+
+	// CHANGE COLUMN
+	s.testParallelExecSQL(c, "alter table test_exists change column if exists a c int") // only, `c` exists now
+
+	// MODIFY COLUMN
+	s.testParallelExecSQL(c, "alter table test_exists modify column if exists a bigint")
+
+	// DROP INDEX
+	_, err = s.se.Execute(context.Background(), "alter table test_exists add index idx_c (c)")
+	c.Assert(err, IsNil)
+	s.testParallelExecSQL(c, "alter table test_exists drop index if exists idx_c")
+
+	// DROP PARTITION (ADD PARTITION tested in TestParallelAlterAddPartition)
+	_, err = s.se.Execute(context.Background(), "create table test_exists_2 (a int key) partition by range(a) (partition p0 values less than (10), partition p1 values less than (20))")
+	c.Assert(err, IsNil)
+	s.testParallelExecSQL(c, "alter table test_exists_2 drop partition if exists p1")
+}
+
 // TestParallelDDLBeforeRunDDLJob tests a session to execute DDL with an outdated information schema.
 // This test is used to simulate the following conditions:
 // In a cluster, TiDB "a" executes the DDL.

ddl/db_test.go

@@ -2641,6 +2641,78 @@ func (s *testDBSuite4) TestAddColumn2(c *C) {
 	s.tk.MustQuery("select a,b,_tidb_rowid from t2").Check(testkit.Rows("1 3 2"))
 }
 
+func (s *testDBSuite4) TestIfNotExists(c *C) {
+	s.tk = testkit.NewTestKit(c, s.store)
+	s.tk.MustExec("use test_db")
+	s.mustExec(c, "drop table if exists t1")
+	s.mustExec(c, "create table t1 (a int key);")
+
+	// ADD COLUMN
+	sql := "alter table t1 add column b int"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrDupFieldName)
+	s.mustExec(c, "alter table t1 add column if not exists b int")
+
+	// ADD INDEX
+	sql = "alter table t1 add index idx_b (b)"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrDupKeyName)
+	s.mustExec(c, "alter table t1 add index if not exists idx_b (b)")
+
+	// CREATE INDEX
+	sql = "create index idx_b on t1 (b)"
+	assertErrorCode(c, s.tk, sql, tmysql.ErrDupKeyName)
+	s.mustExec(c, "create index if not exists idx_b on t1 (b)")
+
+	// ADD PARTITION
+	s.mustExec(c, "drop table if exists t2")
+	s.mustExec(c, "create table t2 (a int key) partition by range(a) (partition p0 values less than (10), partition p1 values less than (20))")
+	sql = "alter table t2 add partition (partition p2 values less than (30))"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrSameNamePartition)
+	s.mustExec(c, "alter table t2 add partition if not exists (partition p2 values less than (30))")
+}
+
+func (s *testDBSuite4) TestIfExists(c *C) {
+	s.tk = testkit.NewTestKit(c, s.store)
+	s.tk.MustExec("use test_db")
+	s.mustExec(c, "drop table if exists t1")
+	s.mustExec(c, "create table t1 (a int key, b int);")
+
+	// DROP COLUMN
+	sql := "alter table t1 drop column b"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrCantDropFieldOrKey)
+	s.mustExec(c, "alter table t1 drop column if exists b") // only `a` exists now
+
+	// CHANGE COLUMN
+	sql = "alter table t1 change column b c int"
+	assertErrorCode(c, s.tk, sql, tmysql.ErrBadField)
+	s.mustExec(c, "alter table t1 change column if exists b c int")
+	s.mustExec(c, "alter table t1 change column if exists a c int") // only `c` exists now
+
+	// MODIFY COLUMN
+	sql = "alter table t1 modify column a bigint"
+	assertErrorCode(c, s.tk, sql, tmysql.ErrBadField)
+	s.mustExec(c, "alter table t1 modify column if exists a bigint")
+	s.mustExec(c, "alter table t1 modify column if exists c bigint") // only `c` exists now
+
+	// DROP INDEX
+	s.mustExec(c, "alter table t1 add index idx_c (c)")
+	sql = "alter table t1 drop index idx_c"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrCantDropFieldOrKey)
+	s.mustExec(c, "alter table t1 drop index if exists idx_c")
+
+	// DROP PARTITION
+	s.mustExec(c, "drop table if exists t2")
+	s.mustExec(c, "create table t2 (a int key) partition by range(a) (partition p0 values less than (10), partition p1 values less than (20))")
+	sql = "alter table t2 drop partition p1"
+	s.mustExec(c, sql)
+	assertErrorCode(c, s.tk, sql, tmysql.ErrDropPartitionNonExistent)
+	s.mustExec(c, "alter table t2 drop partition if exists p1")
+}
+
 func (s *testDBSuite5) TestAddIndexForGeneratedColumn(c *C) {
 	s.tk = testkit.NewTestKit(c, s.store)
 	s.tk.MustExec("use test_db")

ddl/ddl.go

@@ -241,8 +241,8 @@ type DDL interface {
 	RecoverTable(ctx sessionctx.Context, tbInfo *model.TableInfo, schemaID, autoID, dropJobID int64, snapshotTS uint64) (err error)
 	DropView(ctx sessionctx.Context, tableIdent ast.Ident) (err error)
 	CreateIndex(ctx sessionctx.Context, tableIdent ast.Ident, unique bool, indexName model.CIStr,
-		columnNames []*ast.IndexColName, indexOption *ast.IndexOption) error
-	DropIndex(ctx sessionctx.Context, tableIdent ast.Ident, indexName model.CIStr) error
+		columnNames []*ast.IndexColName, indexOption *ast.IndexOption, ifNotExists bool) error
+	DropIndex(ctx sessionctx.Context, tableIdent ast.Ident, indexName model.CIStr, ifExists bool) error
 	AlterTable(ctx sessionctx.Context, tableIdent ast.Ident, spec []*ast.AlterTableSpec) error
 	TruncateTable(ctx sessionctx.Context, tableIdent ast.Ident) error
 	RenameTable(ctx sessionctx.Context, oldTableIdent, newTableIdent ast.Ident, isAlterTable bool) error