mysql - 使用变量作为名称删除外键

Question

我使用以下内容:

DECLARE @ConstraintName varchar(255);
SELECT @ConstraintName = CONSTRAINT_NAME 
FROM 
   INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE 
WHERE 
   TABLE_NAME = 'TheTable' 
   AND COLUMN_NAME = 'TheColumn';

alter table TheTable drop constraint @ConstraintName;

但是，@ConstraintName 附近的语法不正确。这可能是一件小事，但我无法弄清楚。我应该改变什么才能取消约束？

SQLFiddle:http://sqlfiddle.com/#!2/6709e/3

Answer 1

DECLARE @constraintName VARCHAR(50);
DECLARE @runString VARCHAR(2000);

select @constraintName = CONSTRAINT_NAME
from INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE
WHERE TABLE_NAME = 'TheTable' AND COLUMN_NAME = 'TheColumn';


SET @runString = CONCAT('ALTER TABLE TheTable DROP CONSTRAINT ', @constraintName);
PREPARE stmt1 FROM @runString ;
EXECUTE stm1;
DEALLOCATE PREPARE stmt1;