To change the data type of a column in a table, use the following syntax: SQL Server / MS Access: ALTER TABLE table_name ALTER COLUMN column_name datatype My SQL / Oracle: ALTER TABLE table_nameMODIFY column_name datatype 增加约束. alter table table_nameaddconstraint 约束名称增加的约束类...
In MySQL, the ALTER TABLE statement is used to modify an existing table. One of the most common modifications is adding a new column to a table. This article will explain how to use the ALTER TABLE statement with the ADD clause to add a new column to an existing MySQL table. 2. Synt...
Syntax:ALTER,TABLE,table,ADD,field,COLUMN,type[(size)] [NOT,NULL],[CONSTRAINT,index] ALTER,TABLE,table,ADD,CONSTRAINT,multifieldindex ALTER,TABLE,table,DROP,COLUMN,field ALTER,TABLE,table,DROP,CONSTRAINT,indexname Explanation:thetableparameterisusedtospecifythename ...
Syntax for out-of-line constraints CREATE TABLE <name> ... ( <col1_name> <col1_type> [ , <col2_name> <col2_type> , ... ] [ , { outoflineUniquePK | outoflineFK } ] [ , { outoflineUniquePK | outoflineFK } ] [ , ... ] ) ALTER TABLE <name> ... ADD { outof...
alter tabel table_name add column_name datatype; 删除列: alter tabel table_namedrop columncolumn_name; 要改变表中列的数据类型,不同的系统命令不同: To change the data type of a column in a table, use the following syntax: SQL Server / MS Access: ...
constraint CK_字段 check(约束。如:len(字段)>1), -- 主外键关系 constraint FK_主表_从表 foreign(外键字段) references 主表(主表主键字段) 8)添加/创建索引 alter table 表名 add index 索引名 列名; # 普通索引 ALTER TABLE 表名 ADD UNIQUE index 索引名 (列名1,列名2); # 联合索引 ...
Syntax ALTER TABLE table_name { RENAME TO clause | ADD COLUMN clause | ALTER COLUMN clause | DROP COLUMN clause | RENAME COLUMN clause | DEFAULT COLLATION clause | ADD CONSTRAINT clause | DROP CONSTRAINT clause | DROP FEATURE clause | ...
Common Syntax: ALTER TABLE <tbl_name>[ [alter_table_commands] ... [alter_partition_function] ...]ALTER TABLE <tbl_name>LAZY PROTECT[REPLICAS [=] <value>]ALTER TABLE <tbl_name>DROP PARTITION [ ALL | <col_list> [, <col_list> ...] ]ALTER TABLE <tbl_name>TRUNCATE PARTITION [ ALL...
ALTERTABLEadb_demo.customer MODIFYCOLUMNlogin_timeTIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMP; Change the value constraint for a column to NULL Syntax ALTERTABLEdb_name.table_name MODIFY [COLUMN] column_name column_type {NULL} Usage notes You can change the value constraint for a column from NOT NUL...
alter 语法(Alter syntax) Usage of the alter statement Usage of the alter statement If you need to modify the structure, use the alter statement, as follows: The ALTER TABLE statement is used to modify the design of the existing table. Syntax: ALTER, TABLE, table, ADD, field, COLUMN, typ...