ALTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...); DROP CONSTRAINT (删除约束),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; DROP PRIMARY KEY (删除主键),语...
ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyPrimaryKey; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP PRIMARY KEY...
ALTERTABLEtable_nameADDCONSTRAINTMyPrimaryKeyPRIMARYKEY(column1, column2...); DROP CONSTRAINT (删除约束),语法如下: ALTERTABLEtable_nameDROPCONSTRAINTMyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTERTABLEtable_nameDROPINDEXMyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: ALTERTABLEtable_name...
ALTER TABLE table_name ADD CONSTRAINTMyPrimaryKeyPRIMARY KEY(column1,column2...); DROP CONSTRAINT (删除约束),语法如下: ALTER TABLE table_name DROP CONSTRAINTMyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEXMyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: A...
删除约束 删除约束通常需要知道它的名称,可以通过psql工具的\d table_name命令查看表的约束。 ALTER TABLE table_name DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]; RESTRICT是默认值,如果存在
DROP CONSTRAINT (删除约束),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; 1. 2. 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; 1. 2. DROP PRIMARY KEY (删除主键),语法如下: ALTER TABLE table_name ...
公式:alter table 表名 add constraint yy primary key(主键1,主键2); 1. 2. 2)有命名主键的删除 ALTER TABLE table_test DROP CONSTRAINT yy; 公式:ALTER TABLE 表名DROP CONSTRAINT 主键名; 1. 2. 3)有命名主键的修改 需先删除主键,再进行添加 ...
ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyPrimaryKey; 如果是 MYSQL ,代码是这样: ...
ALTER TABLE 表名 DROP CONSTRAINT 约束名; 示例: ALTER TABLE students DROP CONSTRAINT unique_email; (3)添加非空约束: ALTER TABLE 表名 ALTER COLUMN 字段名 SET NOT NULL; 示例: ALTER TABLE students ALTER COLUMN student_name SET NOT NULL; ...