ALTERTABLEemployees MODIFYCOLUMNsalaryDECIMAL(10,2); 4.2 修改列的默认值 要更改列的默认值,可以使用以下语法: ALTERTABLEtable_nameALTERCOLUMNcolumn_nameSETDEFAULTdefault_expression; 要移除列的默认值,可以使用: ALTERTABLEtable_nameALTERCOLUM
ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT} 准备测试数据 DROPTABLEtb001;CREATETABLEtb001(idINTauto_incrementPRIMARYKEY,c1VARCHAR(20));INSERTINTOtb001(c1)SELECTuserFROMmysql.user; 测试MODIFY COLUMN ALTERTABLEtb001 MODIFYCOLUMNC1VARCHAR(20)NOTNULLDEFAULT'A1'; 测试ALTER COLUMN ALTER...
ALTERTABLEtestMODIFYCOLUMNnameVARCHAR(20); -- 改变列的默认值 ALTERTABLEtestMODIFYCOLUMNnameVARCHAR(20)NOTNULLDEFAULT'a'; -- 删除列的默认值 ALTERTABLEtest MODIRYCOLUMNnameVARCHAR(20); CHANGE COLUMN:重命名列;重命名列和修改列的数据类型(备注:单独修改列的数据类型报错)。 1 2 3 4 5 -- 重命名列...
ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL FIRST; ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL AFTER baz; 1. 2. MODIFY COLUMN 语法: 1. MODIFY [COLUMN] col_name column_definition [FIRST | AFTER col_name] 1. 作用: 除了列的重命名之外,他干的活和...
ALTER TABLE table_name ADD COLUMN new_column_name datatype; 以下SQL 语句在 employees 表中添加了一个名为 birth_date 的日期列: 实例 ALTERTABLEemployees ADDCOLUMNbirth_dateDATE; 2. 修改列的数据类型 实例 ALTERTABLETABLE_NAME MODIFYCOLUMNcolumn_name new_datatype; ...
5.6中,发现其实alter column 和更改modify column 步骤是一样的 mysql>create table xs(name varchar(12),age int default 5); Query OK, 0 rows affected (0.34 sec) mysql>insert into xs values('a',4); Query OK, 1 row affected (0.05 sec) ...
To rename a column, MySQL provides syntax: ALTER TABLE CHANGE ... which requires re-specification of all the attributes of the column. Disadvantages of the above syntax : - All the column information might not be available to the application trying to do the rename. - There is a risk of...
ALTER TABLEMODIFY子命令主要用于修改现有列的数据类型或约束，而不改变列的名称。该命令适用于当需要调整列的长度、数据类型（如从INT改为VARCHAR）、或添加NOTNULL约束等场景。语法结构相对简单，基本格式为ALTERTABLE table_name MODIFY column_name new_data_type[constraints];。例如，假设有一个名为employees的表，...
Operations that modify table metadata only. These operations are immediate because the server does not touch table contents. Metadata-only operations include: Renaming a column. In NDB Cluster, this operation can also be performed online. Changing the default value of a column (except for NDB ...
ALTER TABLE <表名> [修改选项]修改选项的语法格式如下：{ ADD COLUMN <列名> <类型> | CHANGE COLUMN <旧列名> <新列名> <新列类型> | ALTER COLUMN <列名> { SET DEFAULT <默认值> | DROP DEFAULT } | MODIFY COLUMN <列名> <类型> | DROP COLUMN <列名> | RENAME TO <新表名> } 添加字段 ...