CONSTRAINT p_id_fk FOREIGN KEY(id) REFERENCES person(id) ); 2.7 级联操作 级联修改: ON UPDATE CASCADE 级联删除: ON DELETE CASCADE -- 声明一个外键约束 CONSTRAINT emlyee_dept_fk FOREIGN KEY(deptId) REFERENCES dept(id) ON UPDATE CASCADE ON DELETE CASCADE -- 外键名称 外键 参考表(参考字段) 3...
Function object to remove a foreign key constraint from the referenced_set of the referenced table. The foreign key object is also removed from the dictionary cache. The foreign key constraint is not removed from the foreign_set of the table containing the constraint. ...
CREATE TABLE major( id INT PRIMARY KEY, major_name VARCHAR(20) ); DROP TABLE IF EXISTS myStuinfo; CREATE TABLE myStuinfo( id INT PRIMARY KEY AUTO_INCREMENT, cname VARCHAR(20), majorId INT, CONSTRAINT majorid_to_major FOREIGN KEY (majorid) REFERENCES major(id) ON DELETE CASCADE ); 1. ...
(errno: 152) now, i try to remove the constraint by it's constraint name: mysql> alter table test drop foreign key FKref_ID; ERROR 1025 (HY000): Error on rename of '.\eltas\test' to '.\eltas\#sql2-704-2' (errno: 152) mysql> select version(); +---+ | version() | +-...
Assume we want to drop the UNIQUE constraint on the "Address" column, and the name of the constraint is "Con_First." To do this, we type in the following: MySQL: ALTER TABLE Customer DROP INDEX Con_First;Note that MySQL uses DROP INDEX for index-type constraints such as UNIQUE. ...
MySQL allows table columns to be created with the NOT NULL constraint. This implies that the field needs to be populated with a value that cannot be the NULL value. In some cases we may need to remove this constraint. This is achieved using the following command: ...
In MySQL, the syntax for ALTER TABLE Drop Column is, ALTER TABLE "table_name" DROP "column_name"; In Oracle, SQL Server, and Google BigQuery, the syntax for ALTER TABLE Drop Column is, ALTER TABLE "table_name" DROP COLUMN "column_name"; Let...
In this post we look at ways to remove all duplicate rows except one in an SQL database. For all examples in this article, we'll be using the following MySQL "user" table: +---+---+|id|name|+---+---+|1|john||2|david||3|john||4|john||5|wayne||6|david|+---+---+...
Can a column act as both primary key and foreign key Can a web service return an HTML formatted file? Can I comment on web.config? Can I convert Windows Form to Web Form? can i do div display:none; from c# code behind? can I get all public variables in a class? can I get value...
Can't Enable Foreign Key Constraint (Msg 547, Level 16, State 0, Line 15) Can't perform emptyfile operation on .mdf? Can't select DISTINCT values with XML datatype. Can't use Begin Transaction before a WITH Cancel Rollback Cannot ALTER 'dbo.fn_GetDate' because it is being referenced...