fix(mtr): add test case for add column.(#1140)

Add test case: when alter table xxx add colmn operation is failed firstly, executing
alter table xxx add colmn by successful case again

mysql-test/suite/tianmu/r/alter_column.result

@@ -39,4 +39,26 @@ NULL	2	b	NULL	NULL
 NULL	3	c	NULL	NULL
 NULL	4	d	NULL	NULL
 NULL	5	e	NULL	NULL
+CREATE TABLE st1 (
+task_id INT NOT NULL,
+subject VARCHAR(45) NULL,
+start_date DATE NULL,
+end_date DATE NULL,
+description VARCHAR(200) NULL,
+PRIMARY KEY (task_id)
+);
+ALTER TABLE st1 ADD COLUMN test numeric(20,10);
+ERROR HY000: Unable to inplace alter table
+ALTER TABLE st1 ADD COLUMN test1 numeric(8,2);
+SHOW CREATE TABLE st1;
+Table	Create Table
+st1	CREATE TABLE `st1` (
+  `task_id` int(11) NOT NULL,
+  `subject` varchar(45) DEFAULT NULL,
+  `start_date` date DEFAULT NULL,
+  `end_date` date DEFAULT NULL,
+  `description` varchar(200) DEFAULT NULL,
+  `test1` decimal(8,2) DEFAULT NULL,
+  PRIMARY KEY (`task_id`)
+) ENGINE=TIANMU DEFAULT CHARSET=latin1
 DROP DATABASE alter_colunm;

mysql-test/suite/tianmu/t/alter_column.test

@@ -56,5 +56,25 @@ ALTER TABLE t1 DROP COLUMN c11;
 SHOW CREATE TABLE t1;
 SELECT * FROM t1 ORDER BY c1;
 
+#################
+# ADD  COLUMEN BEFORE THE FIRST ADDING COLUMN IS WRONG
+#################
+
+CREATE TABLE st1 (
+    task_id INT NOT NULL,
+    subject VARCHAR(45) NULL,
+    start_date DATE NULL,
+    end_date DATE NULL,
+    description VARCHAR(200) NULL,
+    PRIMARY KEY (task_id)
+);
+
+--error 6
+ALTER TABLE st1 ADD COLUMN test numeric(20,10);
+
+ALTER TABLE st1 ADD COLUMN test1 numeric(8,2);
+
+SHOW CREATE TABLE st1;
+
 # Clean UP
 DROP DATABASE alter_colunm;

storage/tianmu/core/value_set.cpp

@@ -154,7 +154,6 @@ void ValueSet::Add(const types::TianmuValueObject &rcv) {
   if (rcv.IsNull())
     contains_nulls = true;
   else {
-    // Add(rcv.Get()->Clone());
     std::unique_ptr<types::TianmuDataType> tianmu_dt = rcv.Get()->Clone();
     if (tianmu_dt->IsNull()) {
       contains_nulls = true;