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ALTER TABLE__数据定义语言_SQL语法参考_云数据库 OceanBase-阿里云

该语句用于修改已存在的表的结构，比如：修改表及表属性、新增列、修改列及属性、删除列等。

格式

  1. ALTER TABLE tblname
  2.     alter_specification [, alter_specification]... ;
  4. alter_specification: 
  5.    ADD [COLUMN] colname column_definition 
  6.   | ADD [COLUMN] (colname column_definition,...) 
  7.   | ADD [UNIQUE]{INDEX|KEY} [indexname] (index_col_name,...) [index_options]
  8.   | ADD PRIMARY KEY (index_col_name,...) [index_options](暂不支持)
  9.   | ALTER [COLUMN] colname {SET DEFAULT literal | DROP DEFAULT}
  10.   | CHANGE [COLUMN] oldcolname newcolname column_definition
  11.   | MODIFY [COLUMN] colname column_definition  
  12.   | DROP [COLUMN] colname
  13.   | DROP PRIMARY KEY (暂不支持)
  14.   | DROP {INDEX | KEY} indexname
  15.   | RENAME [TO] newtblname
  16.   | ORDER BY colname (暂不支持)
  17.   | CONVERT TO CHARACTER SET charsetname [COLLATE collationname] (暂不支持)
  18.   | [DEFAULT] CHARACTER SET charsetname [COLLATE collationname] (暂不支持)
  19.   | table_options
  20.   | partition_options
  21.   | DROP TABLEGROUP 
  22.   | AUTO_INCREMENT [=] num
  24. column_definition: 
  25.      data_type [NOT NULL | NULL] [DEFAULT defaultvalue] 
  26.       [AUTO_INCREMENT] [UNIQUE [KEY]](暂不支持) [[PRIMARY] KEY] (暂不支持)
  27.       [COMMENT 'string'] 
  29. table_options: 
  30.      [SET] table_option [[,] table_option]... 
  32. table_option: 
  33. [DEFAULT] {CHARACTER SET | CHARSET} [=] charsetname
  34. | [DEFAULT] COLLATE [=] collationname
  35. | COMMENT [=] 'string' 
  36. | COMPRESSION [=] '{NONE | LZ4_1.0 | LZO_1.0 | SNAPPY_1.0 |ZLIB_1.0}'
  37. | EXPIRE_INFO [=] (expr)
  38. | REPLICA_NUM [=] num
  39. | TABLE_ID [=] id
  40. | BLOCK_SIZE [=] size
  41. | USE_BLOOM_FILTER [=] {True | False}
  42. | PROGRESSIVE_MERGE_NUM [=] num
  43. | TABLEGROUP [=] tablegroupname
  44. | PRIMARY_ZONE [=] zone 
  45. | AUTO_INCREMENT [=] num
  46. partition_options: 
  47.      PARTITION BY
  48.          HASH(expr) 
  49.          | KEY(column_list) 
  50.          [PARTITIONS num] 
  51.          [partition_definition ...]
  53. partition_definition: 
  54.      COMMENT [=] 'commenttext' (暂不支持)

增加列

  1. ALTER TABLE tblname 
  2.     ADD [COLUMN] colname data_type 
  3.     [NOT NULL | NULL] 
  4.     [DEFAULT defaultvalue];

修改列属性

  1. ALTER TABLE tblname
  2.    ALTER [COLUMN] colname 
  3.    [SET DEFAULT literal| DROP DEFAULT];

修改列类型

  1. ALTER TABLE tblname
  2.     MODIFY colname column_definition;

删除列

  1. ALTER TABLE tblname
  2.     DROP [COLUMN] colname;
  • 不允许删除主键列或者包含索引的列。

表重命名

  1. ALTER TABLE tblname
  2.    RENAME TO newtblname;

列重命名

  1. ALTER TABLE tblname
  2.     CHANGE [COLUMN] oldcolname newcolname column_definition;

注意：

  1. 对于varchar类型的列，只允许将varchar的长度变大，不允许减小。
  2. 在 OceanBase 0.5 里列重命名是用 ALTER TABLE tblname RENAME [COLUMN] oldcolname TO newcolname，OceanBase 1.0的实现与MySQL兼容。

例1：

  1. #把表t2的字段d改名为c，并同时修改了字段类型
  2. ALTER TABLE t2 CHANGE COLUMN d c CHAR(10);

设置过期数据删除

  1. ALTER TABLE tblname
  2.     SET EXPIRE_INFO [ = ] expr;

例2：

  1. CREATE TABLE example_1(custid INT            
  2.     , thedate TIMESTAMP
  3.     , cost INT 
  4.     , PRIMARY KEY(custid, thedate)
  5.     ) EXPIRE_INFO = (thedate < date_sub(merging_frozen_time(), INTERVAL 2 DAY)), 
  6.     USE_BLOOM_FILTER = FALSE;

(thedate < date_sub(merging_frozen_time(), INTERVAL 2 DAY))，表示删除（过期）thedate字段值为冻结时间2天前的数据，删除数据动作在数据合并时候真正执行。

修改过期条件

  1. # 删除（过期）thedate字段值为1天前的数据。
  2. alter table example_1 set EXPIRE_INFO = (thedate < date_sub(merging_frozen_time(), INTERVAL 1 DAY))

设置Partition表BLOCK大小

  1. ALTER TABLE tblname
  2.     SET BLOCK_SIZE [=] blocksize;

设置该表的副本数

  1. ALTER TABLE tblname
  2.     SET REPLICA_NUM [=] num;

这里是指表的副本总数多少。

设置该表的压缩方式

  1. ALTER TABLE tblname
  2.     SET COMPRESSION [=] '{NONE | LZ4_1.0 | LZO_1.0 | SNAPPY_1.0 | ZLIB_1.0}';

设置是否使用BloomFilter

  1. ALTER TABLE tblname
  2.     SET USE_BLOOM_FILTER [=] {True | Flase};

设置注释信息

  1. ALTER TABLE tblname
  2.     SET COMMENT [=] 'commentstring';

设置渐进合并步数

  1. ALTER TABLE tblname
  2.   SET PROGRESSIVE_MERGE_NUM [=] num;

此功能是设置渐近合并步数，PROGRESSIVE_MERGE_NUM现在在限制是1~64。

设置表的ZONE属性

  1. ALTER TABLE tblname
  2.     zone_specification...;
  4. zone_specification: 
  5.     PRIMARY_ZONE [=] zone

修改AUTO_INCREMENT字段的起始值

可在create talbe时指定AUTO_INCREMENT的起始值，也可用alter table tbl_name AUTO_INCREMENT=n命令来重设自增的起始值，但是如果设置的n比AUTO_INCREMENT字段的当前值小的话，执行的sql不会报错，但是不会生效！

  1. Oceanbase>create table t1(id int auto_increment primary key,name varchar(10)) auto_increment=100;
  2. Query OK, 0 rows affected (0.10 sec)
  4. Oceanbase>alter table t1 auto_increment=50;
  5. Query OK, 0 rows affected (0.04 sec)
  6. #用alter table语句把t1表的auto_increment起始值调整为50,由于50小于100，修改无效
  8. Oceanbase>show create table t1;
  9. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  10. | Table | Create Table                                                                                                                                                                                                                     |
  11. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  12. | t1    | CREATE TABLE `t1` (
  13.   `id` int(11) NOT NULL AUTO_INCREMENT,
  14.   `name` varchar(10) DEFAULT NULL,
  15.   PRIMARY KEY (`id`)
  16. ) AUTO_INCREMENT = 100 DEFAULT CHARSET = utf8mb4 REPLICA_NUM = 3 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE |
  17. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  19. Oceanbase>alter table t1 auto_increment=110;
  20. Query OK, 0 rows affected (0.03 sec)
  22. Oceanbase>show create table t1;
  23. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  24. | Table | Create Table                                                                                                                                                                                                                     |
  25. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  26. | t1    | CREATE TABLE `t1` (
  27.   `id` int(11) NOT NULL AUTO_INCREMENT,
  28.   `name` varchar(10) DEFAULT NULL,
  29.   PRIMARY KEY (`id`)
  30. ) AUTO_INCREMENT = 110 DEFAULT CHARSET = utf8mb4 REPLICA_NUM = 3 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE |
  31. +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  32. 1 row in set (0.01 sec)

最后更新：2016-11-24 11:23:47

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