Dropping foreign key using variable as name

Question

I use the following:

DECLARE @ConstraintName varchar(255);
SELECT @ConstraintName = CONSTRAINT_NAME 
FROM 
   INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE 
WHERE 
         


        

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;

Answer 2

Try this

SELECT CONSTRAINT_NAME INTO @ConstraintName 
FROM 
   INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE 
WHERE 
   TABLE_NAME = 'TheTable' 
   AND COLUMN_NAME = 'TheColumn';

SET @queryStr = CONCAT('alter table TheTable drop constraint ', @ConstraintName);
PREPARE qry from @queryStr;
EXECUTE qry;

For more information: https://dev.mysql.com/doc/refman/5.7/en/execute.html

Answer 3

Try this :

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

alter table TheTable drop constraint @ConstraintName;

Or :

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;