ALTER TABLE

Purpose

You can use this statement to modify the structure of an existing table. For example, you can use this statement to modify a table and its attributes, add columns to it, modify its columns and attributes, and drop its columns.

Syntax

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]] 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)
    | ADD {INDEX | KEY} [index_name] [index_type] (key_part,...) [index_option_list][index_column_group_option]
    | ADD COLUMN GROUP([all columns, ]each column)
    | 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
    | DROP COLUMN GROUP([all columns, ]each column)
    | MODIFY [COLUMN] column_definition
    | RENAME COLUMN old_col_name TO new_col_name
    | RENAME [TO] table_name
    | RENAME {INDEX | KEY} old_index_name TO new_index_name
    | [SET] table_option_list
    | TRUNCATE {PARTITION | SUBPARTITION} partition_name_list
    | EXCHANGE PARTITION partition_name WITH TABLE non_partition_table_name WITHOUT VALIDATION

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 string_value] [SKIP_INDEX(skip_index_option_list)] [ opt_position_column ]

skip_index_option_list:
    skip_index_option [,skip_index_option ...]

skip_index_option:
    MIN_MAX
    | SUM

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 NULL | NO ACTION | SET DEFAULT}

column_desc_list:
    column_desc [, column_desc ...]

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

key_part:
    {index_col_name [(length)] | (expr)} [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 string_value

index_column_group_option:
    WITH COLUMN GROUP([all columns, ]each column)

table_option_list:
    table_option [ table_option ...]

table_option:
      TABLEGROUP = tablegroup_name
    | block_size
    |lob_inrow_threshold [=] num
    | compression
    | AUTO_INCREMENT [=] INT_VALUE
    | COMMENT string_value
    | parallel_clause

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

Parameters

Examples

Add and drop columns

Create a table named tbl1 and execute the DESCRIBE statement to view the table information.

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    |       |   
+-------+------------+----------+--------+---------+-------+

• Add a column named c3 and execute the DESCRIBE statement to view the table information.

  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
  

• Drop the c3 column and execute the DESCRIBE statement to view the table information.

  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
  

• Rename the c2 column in the tbl1 table to c3 and execute the DESCRIBE statement to view the table information.

  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
  

• Add a column named c4 to the tbl1 table, set this column as the first column of the table, and execute the DESCRIBE statement to view the table information.

  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
  

• Add a column named c2 behind the c1 column and execute the DESCRIBE statement to view the table information.

  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
  

• Add a column named c5 before the c4 column and execute the DESCRIBE statement to view the table information.

  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
  

• Add a FOREIGN KEY constraint fk1 to the tbl2 table. Specify to execute the SET NULL action when an UPDATE operation affects a key value in the parent table that has matching rows in the child table.

  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) ON UPDATE SET NULL;
  Query OK, 0 row affected
  

• Drop the FOREIGN KEY constraint fk1 from the tbl3 table.

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

• Drop the primary key of the tbl2 table.

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

Index operations

• Rename the ind1 index on the tbl2 table to 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
  

• Create an index named ind3 on the tbl2 table to reference the c1 and c2 columns.

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

  You can execute the SHOW INDEX statement to view the created indexes.

  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
  

• Drop the ind2 index from the tbl2 table.

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

  Note

  You can use the preceding method to implement an atomic change to an index in actual O&M scenarios.

• Add three function-based indexes to t1_func, name one index as i2, and use system-generated names in the format of a sequence number prefixed with functional_index for the other two indexes.

  obclient> ALTER TABLE t1_func ADD INDEX ((CONCAT(c1,'a')));
  Query OK, 0 rows affected
  obclient> ALTER TABLE t1_func ADD INDEX ((c1+1));
  Query OK, 0 rows affected
  obclient> ALTER TABLE t1_func ADD INDEX i2 ((CONCAT(c1,'a')));
  Query OK, 0 rows affected
  obclient> SHOW CREATE TABLE t1_func;
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table   | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | t1_func | CREATE TABLE `t1_func` (
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  KEY `i1` (((`c1` + `c2`) < 1)) BLOCK_SIZE 16384 LOCAL,
  KEY `functional_index` (concat(`c1`,'a')) BLOCK_SIZE 16384 LOCAL,
  KEY `functional_index_2` ((`c1` + 1)) BLOCK_SIZE 16384 LOCAL,
  KEY `i2` (concat(`c1`,'a')) BLOCK_SIZE 16384 LOCAL
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  

• Create a columnstore index for a table.

  1. Create a table named tbl3.

     CREATE TABLE tbl3 (col1 INT, col2 VARCHAR(50));
     

  2. On the tbl3 table, create a columnstore index named idx1_tbl3 that references the col1 column.

     ALTER TABLE tbl3 ADD INDEX idx1_tbl3 (col1) WITH COLUMN GROUP(each column);
     

Partition operations

• Truncate partitions M202001 and M202002 of the t_log_part_by_range table.

  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
  

• Add the M202006 partition to the t_log_part_by_range table.

  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'))
           );
  

Change the DOP

• Change the DOP of the tbl3 table to 2.

  obclient> ALTER TABLE tbl3 PARALLEL 2;
  

Operations related to column types

• Change the ordinary column col1 of the tbl4 table to an auto-increment column.

  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
  

• Add the primary key column col1 to the tbl4 table, and then change the primary key to 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
  

• Add a CHECK constraint.

  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
  

• Drop the CHECK constraint from the tbl7 table.

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

• Change the column type to 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
  

Rename a column

• RENAME COLUMN only changes the column name and does not change the column definition. If the new column name already exists in the table, an error is reported when RENAME COLUMN is executed. However, no error is reported when the old and new column names are the same.

  obclient> CREATE TABLE tbl8 (a INT, b INT);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl8 RENAME COLUMN a TO b;
  ERROR 1060 (42S21): Duplicate column name 'b'
  
  obclient> ALTER TABLE tbl8 RENAME COLUMN a TO a;
  Query OK, 0 rows affected
  

• If the renamed column has an index, RENAME COLUMN can be executed normally, and the change cascades to the index definition.

  obclient> CREATE TABLE tbl9 (a INT, b INT, index idx_a(a));
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          1 | idx_a    |            1 | a           | A         |        NULL | NULL     | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  1 row in set
  
  obclient> ALTER TABLE tbl9 RENAME COLUMN a TO c;
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          1 | idx_a    |            1 | c           | A         |        NULL | NULL     | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  1 row in set
  

• If the renamed column is referenced by a prefix index, RENAME COLUMN can be executed normally, and the change cascades to the prefix index.

  DROP TABLE tbl9;
  obclient> CREATE TABLE tbl9 (c1 INT PRIMARY KEY, c2 BLOB, c3 INT, INDEX i1 (c2(10)));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl9 RENAME COLUMN c2 TO c2_, RENAME COLUMN c1 TO c2_1;
  DESC tbl9;
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          0 | PRIMARY  |            1 | c2_1        | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     | NULL       |
  | tbl9  |          1 | i1       |            1 | c2_         | A         |        NULL | 10       | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  2 rows in set
  

• If the renamed column has a FOREIGN KEY constraint, RENAME COLUMN can be executed normally, and the change cascades to the FOREIGN KEY constraint.

  obclient> CREATE TABLE tbl10 (a INT PRIMARY KEY);
  Query OK, 0 rows affected
  
  obclient> CREATE TABLE tbl11(b INT, FOREIGN KEY (b) REFERENCES tbl10(a));
  
  obclient> SHOW CREATE TABLE tbl11;
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table | Create Table                                                                                                                                                                                                                                                                                                                                                      |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | tbl11 | CREATE TABLE `tbl11` (
  `b` int(11) DEFAULT NULL,
  CONSTRAINT `tbl11_OBFK_1694681944513338` FOREIGN KEY (`b`) REFERENCES `test`.`tbl10`(`a`) ON UPDATE RESTRICT ON DELETE RESTRICT
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE =  16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  
  obclient> ALTER TABLE tbl10 RENAME COLUMN a TO c;
  Query OK, 0 rows affected
  
  obclient> SHOW CREATE TABLE tbl11;
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table | Create Table                                                                                                                                                                                                                                                                                                                                                      |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | tbl11 | CREATE TABLE `tbl11` (
  `b` int(11) DEFAULT NULL,
  CONSTRAINT `tbl11_OBFK_1694681944513338` FOREIGN KEY (`b`) REFERENCES `test`.`tbl10`(`c`) ON UPDATE RESTRICT ON DELETE RESTRICT
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  

OceanBase Database does not support change or cascading change in the following scenarios:

• The renamed column is referenced by a column generation expression. In this case, an error is reported when you execute RENAME COLUMN.

  obclient> CREATE TABLE tbl12(a INT, b INT AS (a + 1), c INT, d INT, CONSTRAINT d_check CHECK(d > 0)) PARTITION BY HASH(c + 1) PARTITIONS 2;
  
  obclient> ALTER TABLE tbl12 RENAME COLUMN a TO e;
  ERROR 3108 (HY000): Column 'a' has a generated column dependency
  

• The renamed column is referenced by a partition expression. In this case, an error is reported when you execute RENAME COLUMN.

  obclient> ALTER TABLE tbl12 RENAME COLUMN c TO e;
  ERROR 3855 (HY000): Column 'c' has a partitioning function dependency and cannot be dropped or renamed.
  

• The renamed column is referenced by a CHECK constraint. In this case, an error is reported when you execute RENAME COLUMN.

  obclient> ALTER TABLE tbl12 RENAME COLUMN d TO e;
  ERROR 3959 (HY000): Check constraint 'd_check' uses column 'd', hence column cannot be dropped or renamed.
  

• The renamed column is referenced by a function-based index. In this case, an error is reported when you execute RENAME COLUMN.

  DROP TABLE IF EXISTS tbl12;
  obclient> CREATE TABLE tbl12(i INT, INDEX ((i+1)));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl12 RENAME COLUMN i TO j;
  ERROR 3837 (HY000): Column 'i' has a functional index dependency and cannot be dropped or renamed.
  

• The renamed column is referenced by a view. In this case, you can successfully execute RENAME COLUMN, but an error is reported for queries on the view. To solve this problem, you must manually modify the view definition.

  obclient> CREATE TABLE tbl13(a INT);
  Query OK, 0 rows affected
  
  obclient> CREATE VIEW v1 AS SELECT a + 1 FROM tbl13;
  Query OK, 0 rows affected
  
  obclient> SELECT * FROM v1;
  Empty set
  
  obclient> ALTER TABLE tbl13 RENAME COLUMN a TO b;
  Query OK, 0 rows affected
  
  obclient> SELECT * FROM v1;
  ERROR 1356 (42S22): View 'test.v1' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them
  

• The renamed column is referenced by a stored procedure. In this case, you can successfully execute RENAME COLUMN, but an error is reported when the procedure is called. To solve this problem, you must manually modify the stored procedure.

  obclient> CREATE TABLE tbl14(a INT);
  Query OK, 0 rows affected
  
  obclient> CREATE PROCEDURE proc() SELECT a + 1 FROM tbl14;
  Query OK, 0 rows affected
  
  obclient> CALL proc();
  Empty set
  
  obclient> ALTER TABLE tbl14 RENAME COLUMN a TO b;
  Query OK, 0 rows affected
  
  obclient> CALL proc();
  ERROR 1054 (42S22): Unknown column 'a' in 'field list'
  

Modify the columnstore attribute of a table

1. Create a table named tbl1.

   CREATE TABLE tbl1 (col1 INT PRIMARY KEY, col2 VARCHAR(50));
   

2. Convert the tbl1 table into a rowstore-columnstore redundant table, and then drop the rowstore-columnstore redundancy attribute.

   ALTER TABLE tbl1 ADD COLUMN GROUP(all columns, each column);
   

   ALTER TABLE tbl1 DROP COLUMN GROUP(all columns, each column);
   

3. Convert the tbl1 table into a columnstore table, and then drop the columnstore attribute.

   ALTER TABLE tbl1 ADD COLUMN GROUP(each column);
   

   ALTER TABLE tbl1 DROP COLUMN GROUP(each column);
   

Modify the skip index attribute of a column

Use the following SQL statement to create a table named test_skidx.

CREATE TABLE test_skidx(
  col1 INT SKIP_INDEX(MIN_MAX, SUM),
  col2 FLOAT SKIP_INDEX(MIN_MAX),
  col3 VARCHAR(1024) SKIP_INDEX(MIN_MAX),
  col4 CHAR(10)
  );

• Change the type of the skip index on the col2 column in the test_skidx table to SUM.

  ALTER TABLE test_skidx MODIFY COLUMN col2 FLOAT SKIP_INDEX(SUM);
  

• Add the skip index attribute for a column after the table is created.

  Add a skip index of the MIN_MAX type for the col4 column in the test_skidx table.

  ALTER TABLE test_skidx MODIFY COLUMN col4 CHAR(10) SKIP_INDEX(MIN_MAX);
  

• Delete the skip index attribute for a column after the table is created.

  Delete the skip index attribute of the col1 column in the test_skidx table.

  ALTER TABLE test_skidx MODIFY COLUMN col1 INT SKIP_INDEX();
  

  or

  ALTER TABLE test_skidx MODIFY COLUMN col1 INT;
  

References

Modify a table