How to remove check constraint? - sql

Question

I am having difficult to remove CHECK using Alter in sql. Can anyone help me please?
CREATE TABLE MyProject_COST (
ID int(4) NOT NULL UNIQUE,
detail varchar2(25) NOT NULL,
cost int(6) CONSTRAINT cost_project CHECK(cost>=500)
);
ALTER TABLE MyProject_COST ALTER COLUMN Cost int(6)

Answer 1

Oracle does have an alter table ... drop constraint syntax for this.
But since you created an anonymous constraint, so this is tricky - because you don't know the name of the constraint.
One option is to use dynamic SQL to retrieve the constraint name, and drop it with an execute immediate command:
declare
c_name varchar2(255 char);
begin
select c.constraint_name into c_name
from all_constraints c
join all_cons_columns cc
on cc.table_name = c.table_name
and cc.constraint_name = c.constraint_name
where
cc.table_name = 'MYPROJECT_COST'
and cc.column_name ='COST'
and c.constraint_type = 'C' ;
if c_name is not null then
execute immediate
'alter table myproject_cost drop constraint "' || c_name || '"';
end if;
end;
/
Demo on DB Fiddle:
create table myproject_cost (
id int not null unique,
detail varchar2(25) not null,
cost int check(cost >= 500)
);
insert into MyProject_COST(id, detail, cost) values(1, 'foo', 0);
-- ORA-02290: check constraint (FIDDLE_XUVVCZVSYWWROHKPBFUF.SYS_C0030623) violated
declare
c_name varchar2(255 char);
begin
select c.constraint_name into c_name
from all_constraints c
join all_cons_columns cc
on cc.table_name = c.table_name
and cc.constraint_name = c.constraint_name
where
cc.table_name = 'MYPROJECT_COST'
and cc.column_name ='COST'
and c.constraint_type = 'C' ;
if c_name is not null then
execute immediate
'alter table myproject_cost drop constraint "' || c_name || '"';
end if;
end;
/
-- 1 rows affected
insert into MyProject_COST(id, detail, cost) values(1, 'foo', 0);
-- 1 rows affected