*: Support create local temporary table if not exist (#25983)

ddl/db_integration_test.go

@@ -2825,6 +2825,12 @@ func (s *testIntegrationSuite3) TestCreateTemporaryTable(c *C) {
 	tk.MustExec("rollback")
 	tk.MustQuery("select * from check_data").Check(testkit.Rows())
 
+	// Check create temporary table for if not exists
+	tk.MustExec("create temporary table b_local_temp_table (id int)")
+	_, err = tk.Exec("create temporary table b_local_temp_table (id int)")
+	c.Assert(infoschema.ErrTableExists.Equal(err), IsTrue)
+	tk.MustExec("create temporary table if not exists b_local_temp_table (id int)")
+
 	// Stale read see the local temporary table but can't read on it.
 	tk.MustExec("START TRANSACTION READ ONLY AS OF TIMESTAMP NOW(3)")
 	tk.MustGetErrMsg("select * from overlap", "can not stale read temporary table")

executor/ddl.go

@@ -256,7 +256,14 @@ func (e *DDLExec) createSessionTemporaryTable(s *ast.CreateTableStmt) error {
 		sessVars.LocalTemporaryTables = infoschema.NewLocalTemporaryTables()
 	}
 	localTempTables := sessVars.LocalTemporaryTables.(*infoschema.LocalTemporaryTables)
-	return localTempTables.AddTable(dbInfo, tbl)
+	err = localTempTables.AddTable(dbInfo, tbl)
+
+	if err != nil && s.IfNotExists && infoschema.ErrTableExists.Equal(err) {
+		e.ctx.GetSessionVars().StmtCtx.AppendNote(err)
+		return nil
+	}
+
+	return err
 }
 
 func (e *DDLExec) executeCreateView(s *ast.CreateViewStmt) error {