ADD COLUMN

ALTER TABLE.. ADD COLUMN 语句用于在已有表中添加列。在 TiDB 中，ADD COLUMN 为在线操作，不会阻塞表中的数据读写。

语法图

AlterTableStmt:

AlterTableStmt

AlterTableSpec:

AlterTableSpec

ColumnKeywordOpt:

ColumnKeywordOpt

ColumnDef:

ColumnDef

ColumnPosition:

ColumnPosition

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment);

Query OK, 0 rows affected (0.11 sec)

INSERT INTO t1 VALUES (NULL);

Query OK, 1 row affected (0.02 sec)

SELECT * FROM t1;

+----+
| id |
+----+
|  1 |
+----+
1 row in set (0.00 sec)

ALTER TABLE t1 ADD COLUMN c1 INT NOT NULL;

Query OK, 0 rows affected (0.28 sec)

SELECT * FROM t1;

+----+----+
| id | c1 |
+----+----+
|  1 |  0 |
+----+----+
1 row in set (0.00 sec)

ALTER TABLE t1 ADD c2 INT NOT NULL AFTER c1;

Query OK, 0 rows affected (0.28 sec)

SELECT * FROM t1;

+----+----+----+
| id | c1 | c2 |
+----+----+----+
|  1 |  0 |  0 |
+----+----+----+
1 row in set (0.00 sec)