ALTER TABLE

描述

该语句用来修改已存在的表的结构，例如修改表及表属性、新增列、修改列及属性、删除列等。

语法

alter_table_stmt:
      ALTER TABLE table_name alter_table_action_list;

alter_table_action_list:
    alter_table_action [, alter_table_action ...]

alter_table_action: 
      ADD [COLUMN] column_definition  
          [ opt_position_column ]
    | ADD [COLUMN] (column_definition_list)
    | ADD [CONSTRAINT [constraint_name]] {SPATIAL | UNIQUE} {INDEX | KEY} 
          [index_name] index_desc
    | ADD [CONSTRAINT [constraint_name]] FOREIGN KEY
          [index_name] index_desc
          REFERENCES reference_definition
          [match_action][opt_reference_option_list]
    | ADD PRIMARY KEY (column_name)
    | ADD CONSTRAINT [constraint_name] CHECK (expression)[[NOT] ENFORCED]
    | ADD PARTITION (range_partition_list)
    | ALTER [COLUMN] column_name {
          SET DEFAULT const_value 
        | DROP DEFAULT
      }
    | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED
    | ALTER INDEX index_name 
          [VISIBLE | INVISIBLE]
    | CHANGE [COLUMN] column_name column_definition
    | DROP [COLUMN] column_name
    | DROP {PARTITION | SUBPARTITION} partition_name_list
    | DROP TABLEGROUP
    | DROP FOREIGN KEY fk_name
    | DROP PRIMARY KEY [, ADD PRIMARY KEY (column)]
    | DROP CHECK constraint_name
    | MODIFY [COLUMN] column_definition
    | RENAME [TO] table_name
    | RENAME {INDEX | KEY} old_index_name TO new_index_name
    | [SET] table_option_list
    | TRUNCATE {PARTITION | SUBPARTITION} partition_name_list

column_definition_list:
    column_definition [, column_definition ...]

column_definition:
    column_name data_type
    [DEFAULT const_value] [AUTO_INCREMENT]
    [NULL | NOT NULL] [[PRIMARY] KEY] [UNIQUE [KEY]] comment
    [ opt_position_column ]

opt_position_column:
    FIRST | BEFORE | AFTER column_name

index_desc:
   (column_desc_list) [index_type] [index_option_list]

match_action:
   MATCH {SIMPLE | FULL | PARTIAL}

opt_reference_option_list:
   reference_option [,reference_option ...]

reference_option:
   ON {DELETE | UPDATE} {RESTRICT | CASCADE | SET NULLX | NO ACTION | SET DEFAULT}

column_desc_list:
    column_desc [, column_desc ...]

column_desc:
     column_name [(length)] [ASC | DESC]

index_type:
    USING BTREE

index_option_list:
    index_option [ index_option ...]

index_option:
     [GLOBAL | LOCAL]
    | block_size
    | compression
    | STORING(column_name_list)
    | comment

table_option_list:
    table_option [ table_option ...]

table_option:
      table_group
    | block_size
    | compression
    | AUTO_INCREMENT [=] INT_VALUE
    | comment
    | parallel_clause
    | READ {ONLY | WRITE}

parallel_clause:
    {NOPARALLEL | PARALLEL integer}

partition_option:
      PARTITION BY HASH(expression)
      [subpartition_option] PARTITIONS partition_count
    | PARTITION BY KEY([column_name_list])
      [subpartition_option] PARTITIONS partition_count
    | PARTITION BY RANGE {(expression) | COLUMNS (column_name_list)}
      [subpartition_option] (range_partition_list)

subpartition_option:
      SUBPARTITION BY HASH(expression)
      SUBPARTITIONS subpartition_count
    | SUBPARTITION BY KEY(column_name_list)
      SUBPARTITIONS subpartition_count
    | SUBPARTITION BY RANGE {(expression) | COLUMNS (column_name_list)}
      (range_subpartition_list)

range_partition_list:
    range_partition [, range_partition ...]

range_partition:
    PARTITION partition_name
    VALUES LESS THAN {(expression_list) | MAXVALUE}

range_subpartition_list:
    range_subpartition [, range_subpartition ...]

range_subpartition:
    SUBPARTITION subpartition_name
    VALUES LESS THAN {(expression_list) | MAXVALUE}

expression_list:
    expression [, expression ...]

column_name_list:
    column_name [, column_name ...]

partition_name_list:
    partition_name [, partition_name ...]

partition_count | subpartition_count:
    INT_VALUE

参数说明

示例

增加和删除列的操作

创建示例表 tbl1，并执行 DESCRIBE 命令查看表信息。

obclient> CREATE TABLE tbl1 (c1 INT(11) PRIMARY KEY,c2 VARCHAR(50)); 
Query OK, 0 rows affected

obclient> DESCRIBE tbl1; 
+-------+------------+----------+--------+---------+-------+
| Field | Type       | Null     | Key    | Default | Extra | 
+-------+------------+----------+--------+---------+-------+
| c1    | int(11)    | NO       | PRI    | NULL    |       |    
| c2    | varchar(50)| YES      |        | NULL    |       |   
+-------+------------+----------+--------+---------+-------+

• 增加 c3 列，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 ADD c3 INT;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |    
  | c2    | varchar(50)| YES      |        | NULL    |       |  
  | c3    | int(11)    | YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  3 row affected
  

• 删除 c3 列，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 DROP c3;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |    
  | c2    | varchar(50)| YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  2 row affected
  

• 将表 tbl1 的字段 c2 改名为 c3，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 CHANGE COLUMN c2 c3 VARCHAR(50);
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |    
  | c3    | varchar(50)| YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  2 rows affected
  

• 为表 tbl1 添加 c4 列，并将该列设置为表的第一列，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 ADD COLUMN c4 INTEGER FIRST;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c4    | int(11)    | YES      |        | NULL    |       |  
  | c1    | int(11)    | NO       | PRI    | NULL    |       |    
  | c3    | varchar(50)| YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  3 row affected
  

• 在 c1 列后添加 c2 列，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 ADD COLUMN c2 INTEGER AFTER c1;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c4    | int(11)    | YES      |        | NULL    |       |  
  | c1    | int(11)    | NO       | PRI    | NULL    |       | 
  | c2    | int(11)    | YES      |        | NULL    |       |    
  | c3    | varchar(50)| YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  4 row affected
  

• 在 c4 列前添加 c5 列，并执行 DESCRIBE 命令查看表信息。

  obclient> ALTER TABLE tbl1 ADD COLUMN c5 INT BEFORE c4;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1; 
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra | 
  +-------+------------+----------+--------+---------+-------+
  | c5    | int(11)    | YES      |        | NULL    |       |  
  | c4    | int(11)    | YES      |        | NULL    |       |  
  | c1    | int(11)    | NO       | PRI    | NULL    |       | 
  | c2    | int(11)    | YES      |        | NULL    |       |    
  | c3    | varchar(50)| YES      |        | NULL    |       |  
  +-------+------------+----------+--------+---------+-------+
  5 row affected
  

• 为表 tbl2 添加外键约束 fk1。

  obclient> CREATE TABLE tbl2(c1 INT PRIMARY KEY,c2 INT); 
  Query OK, 0 row affected
  obclient> CREATE TABLE tbl3(c1 INT PRIMARY KEY,c2 INT);
  Query OK, 0 row affected
  obclient> ALTER TABLE tbl2 ADD CONSTRAINT fk1 FOREIGN KEY (c2) REFERENCES tbl3(c1);
  Query OK, 0 row affected
  

• 删除 tbl3 表的外键约束 fk1。

  obclient> ALTER TABLE tbl2 DROP FOREIGN KEY fk1;
  Query OK, 0 row affected
  

• 删除 tbl2 表的主键。

  obclient> ALTER TABLE tbl2 DROP PRIMARY KEY;
  Query OK, 0 row affected
  

索引操作

• 将 tbl2 表的索引 ind1 重命名为 ind2。

  obclient> CREATE TABLE tbl2(c1 INT(11) PRIMARY KEY,c2 INT(50));
  Query OK, 0 row affected
  
  obclient> CREATE INDEX ind1 ON tbl2 (c2 ASC);
  Query OK, 0 row affected
  obclient> ALTER TABLE tbl2 RENAME INDEX ind1 TO ind2;
  Query OK, 0 row affected
  

• 在 tbl2 表上创建索引 ind3，引用 c1、c2 列。

  obclient> ALTER TABLE tbl2 ADD INDEX ind3 (c1,c2);
  Query OK, 0 row affected
  

  可以通过 SHOW INDEX 语句查看创建的索引。

  obclient> SHOW INDEX FROM tbl2;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  | tbl2  |          0 | PRIMARY  |            1 | c1          | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind2     |            1 | c2          | A         |        NULL | NULL     | NULL   |  YES | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind3     |            1 | c1          | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind3     |            2 | c2          | A         |        NULL | NULL     | NULL   |  YES | BTREE      | available |               | YES     |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  4 rows in set
  

• 删除 tbl2 表上的索引 ind2。

  obclient> ALTER TABLE tbl2 DROP INDEX ind2;
  Query OK, 0 row affected
  

  说明

  在实际运维场景中，您可以通过以上方式实现索引的原子性变更。

• 创建表 t1_spa 后，在 g 列上创建一个空间索引 t1_g_idx1。

  obclient> CREATE TABLE t1_spa(id INT,name VARCHAR(20),g GEOMETRY NOT NULL SRID 4326);
  Query OK, 0 rows affected
  obclient> ALTER TABLE t1_spa ADD SPATIAL INDEX t1_g_idx1(g);
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM t1_spa;
  +--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table  | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | t1_spa |          1 | t1_g_idx1 |            1 | g           | A         |        NULL | NULL     | NULL   |      | SPATIAL    | available |               | YES     | NULL       |
  +--------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  1 row in set
  

分区操作

• 清除分区表 t_log_part_by_range 的分区 M202001 和 M202002 中的全部数据。

  obclient> CREATE TABLE t_log_part_by_range (
      log_id      bigint NOT NULL 
      , log_value varchar(50)
      , log_date  timestamp NOT NULL  
  ) PARTITION BY RANGE(UNIX_TIMESTAMP(log_date)) 
  (
      PARTITION M202001 VALUES LESS THAN(UNIX_TIMESTAMP('2020/02/01'))
      , PARTITION M202002 VALUES LESS THAN(UNIX_TIMESTAMP('2020/03/01'))
      , PARTITION M202003 VALUES LESS THAN(UNIX_TIMESTAMP('2020/04/01'))
      , PARTITION M202004 VALUES LESS THAN(UNIX_TIMESTAMP('2020/05/01'))
      , PARTITION M202005 VALUES LESS THAN(UNIX_TIMESTAMP('2020/06/01'))
  );
  Query OK, 0 rows affected 
  
  obclient> ALTER TABLE t_log_part_by_range TRUNCATE PARTITION M202001, M202002;
  Query OK, 0 rows affected 
  

• 为分区表 t_log_part_by_range 添加分区 M202006。

  obclient> CREATE TABLE t_log_part_by_range (
      log_id      bigint NOT NULL 
      , log_value varchar(50)
      , log_date  timestamp NOT NULL  
  ) PARTITION BY RANGE(UNIX_TIMESTAMP(log_date)) 
  (
      PARTITION M202001 VALUES LESS THAN(UNIX_TIMESTAMP('2020/02/01'))
      , PARTITION M202002 VALUES LESS THAN(UNIX_TIMESTAMP('2020/03/01'))
      , PARTITION M202003 VALUES LESS THAN(UNIX_TIMESTAMP('2020/04/01'))
      , PARTITION M202004 VALUES LESS THAN(UNIX_TIMESTAMP('2020/05/01'))
      , PARTITION M202005 VALUES LESS THAN(UNIX_TIMESTAMP('2020/06/01'))
  );
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE t_log_part_by_range ADD PARTITION 
           (PARTITION M202006 VALUES LESS THAN(UNIX_TIMESTAMP('2020/07/01'))
           );
  

修改并行度

• 修改表 tbl1 的并行度为 2。

  obclient> ALTER TABLE tbl3 PARALLEL 2;
  

列类型相关操作

• 修改表 tbl4 的普通列 col1 为自增列。

  obclient> CREATE TABLE tbl4 (col1 BIGINT(10) NOT NULL,col2 INT);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl4 MODIFY col1 BIGINT(10) AUTO_INCREMENT;
  Query OK, 0 rows affected
  

• 为表 tbl4 增加主键 col1，之后更改主键为 col2。

  obclient> ALTER TABLE tbl4 ADD PRIMARY KEY (col1);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl4 DROP PRIMARY KEY,ADD PRIMARY KEY (`col2`);
  Query OK, 0 rows affected
  

• 添加 CHECK 约束。

  obclient> CREATE TABLE tbl7(col1 VARCHAR(10),col2 VARCHAR(10));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl7 ADD CONSTRAINT my_check CHECK (col1> col2) ;
  Query OK, 0 rows affected
  

• 删除表 tbl7 的 CHECK 约束。

  obclient> ALTER TABLE tbl7 DROP CHECK my_check;
  Query OK, 0 rows affected
  

• 修改列类型为 NOT NULL。

  obclient> CREATE TABLE dept(  
      deptno           NUMBER(2,0),  
      dname            VARCHAR(14),  
      location         VARCHAR(13),   
      CONSTRAINT pk_dept PRIMARY KEY(deptno)  
  );
  Query OK, 0 rows affected
  
  obclient> CREATE TABLE emp(  
      empno         NUMBER(4,0) NOT NULL,  
      empname       VARCHAR(10) NOT NULL,  
      job           VARCHAR(9) NOT NULL,  
      mgr           NUMBER(4,0) NOT NULL,  
      hiredate      DATE NOT NULL,  
      sal           NUMBER(7,2) DEFAULT NULL, 
      comm          NUMBER(7,2) DEFAULT NULL,        
      deptno        NUMBER(2,0) DEFAULT NULL,   
      CONSTRAINT PK_emp PRIMARY KEY (empno), 
      CONSTRAINT FK_deptno  FOREIGN KEY (deptno)  REFERENCES dept (deptno)  
  );
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE emp MODIFY deptno NUMBER(2,0) DEFAULT '12' NOT NULL;
  Query OK, 0 rows affected