Add constraint if not exists - sql

I want to add the 'check' constraint to some table, but firstly I have to check if that constraint exists. I have some error in my SQL script. What is the corret way to do it ?
ALTER TABLE public.ELEMENTS ADD CONSTRAINT IF NOT EXISTS elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));


According to the manual :
ALTER TABLE ... DROP CONSTRAINT IF EXISTS do exist
ALTER TABLE ... ADD CONSTRAINT IF NOT EXISTS doesn't exist
so you have to execute 1. before 2. :
ALTER TABLE public.ELEMENTS DROP CONSTRAINT IF EXISTS elements_check ;
ALTER TABLE public.ELEMENTS ADD CONSTRAINT elements_check CHECK ((t1_id IS NOT NULL) OR (t2_id IS NOT NULL));

Related

SQL Command (ORACLE) to add constraint with a name

What should be the sql command(oracle) to add 'NOT NULL' constraint, with a constraint name, to a column of existing table?

alter table t add constraint my_named_not_null check ( x is not null );

Can I drop a foreign key without using constraint?

ALTER TABLE table1
ADD FOREIGN KEY attrib1 REFERENCES table2(attrib2)
GO
It works - but how can I drop it?
If I try
DROP FOREIGN KEY (attrib1) REFERENCES table2(attrib2)
it says
Incorrect syntax near the keyword 'FOREIGN'.

In SQL Server you need to drop foreign key constraint by using below query:
Query :
ALTER TABLE [dbo].[Table_Name]
DROP CONSTRAINT [Constraint_Name]
Example:
ALTER TABLE [dbo].[SpeakerDetail]
DROP CONSTRAINT [FK_SpeakerId_UserID]

query to modify the constraint in oracle

I have the below query from oracle query point of view is that I have created a constraint on table BOA_INVOICE as shown below
ALTER TABLE BOA_INVOICE ADD CONSTRAINT CK_INVOICE_SOURCE_SYSTEM CHECK ( SOURCE_SYSTEM IN ('PCE','PDS'));
Now this constraint is added successfully , but later on i want to modify same constraint add two values as shown below
ALTER TABLE BOA_INVOICE ADD CONSTRAINT CK_INVOICE_SOURCE_SYSTEM CHECK ( SOURCE_SYSTEM IN ('PCE','PDS','PER','AWE'));
Please advise what will be the query to achieve the same

You need to drop the constraint first and then create it again.
ALTER TABLE BOA_INVOICE DROP CONSTRAINT CK_INVOICE_SOURCE_SYSTEM;
Then Create it again:
ALTER TABLE BOA_INVOICE ADD CONSTRAINT
CK_INVOICE_SOURCE_SYSTEM CHECK ( SOURCE_SYSTEM IN ('PCE','PDS','PER','AWE'));

How to drop more than one constraint at once (Oracle, SQL)

I'm changing constraints in my database and I need to drop some of them. I know that for a single constraint, the command is following:
ALTER TABLE tblApplication DROP CONSTRAINT constraint1_name;
However, when I try
ALTER TABLE tblApplication DROP (
CONSTRAINT constraint1_name,
CONSTRAINT constraint2_name,
CONSTRAINT constraint3_name
);
it doesn't work and I need to do:
ALTER TABLE tblApplication DROP CONSTRAINT constraint1_name;
ALTER TABLE tblApplication DROP CONSTRAINT constraint2_name;
ALTER TABLE tblApplication DROP CONSTRAINT constraint3_name;
Is there a way to remove more than one constraint in a single command? I'd like to avoid repeating ALTER TABLE tblApplication, just like with the ADD command:
ALTER TABLE tblApplication ADD (
CONSTRAINT contraint1_name FOREIGN KEY ... ENABLE,
CONSTRAINT contraint2_name FOREIGN KEY ... ENABLE,
CONSTRAINT contraint3_name FOREIGN KEY ... ENABLE
);

Yes you can. You just need to repeat 'drop constraint' per constraint. e.g.
alter table t1
drop constraint fk1
drop constraint fk2
/
Edit: I tested this against Oracle 11, and it worked fine. Don't know about older versions.

There is an alternative form to drop constraints related to a column in a table, also dropping the column with CASCADE:
ALTER TABLE table1 DROP (columnName) CASCADE CONSTRAINTS;
It is tested on Oracle 11g

example: we can drop constraints in MySQL by creating constraints to the variables like this way.
create table sample(id int, name varchar(30), marks int, constraint uid unique(id), constraint un unique(name));
alter table sample drop constraint uid, drop constraint un;

Yes, we can drop multiple at once:
ALTER TABLE TABLE NAME
DROP CONSTRAINTS CONSTRAINT VALUE
DROP CONSTRAINTS CONSTRAINT VALUE;

Dropping then adding a constraint fails in oracle

I'm trying to move a primary key constraint to a different column in oracle. I tried this:
ALTER TABLE MY_TABLE
DROP CONSTRAINT c_name;
ALTER TABLE MY_TABLE
ADD CONSTRAINT c_name PRIMARY KEY
(
"COLUMN_NAME"
) ENABLE;
This fails on the add constraint with an error saying the the constraint already exists even though i just dropped it. Any ideas why this is happening

If the original constraint was a primary key constraint, Oracle creates an index to enforce the constraint. This index has the same name as the constraint (C_NAME in your example). You need to drop the index separately from the constraint. So you will need to do a :
ALTER TABLE <table1> DROP CONSTRAINT C_NAME;
DROP INDEX C_NAME;
ALTER TABLE <table1> ADD CONSTRAINT C_NAME PRIMARY KEY
( COLUMN_2 ) ENABLE;

The safest way is to first add a unique index. Try this:
create unique index new_pk on <tabname> (column_2);
Then drop the old PK:
alter table <tabname> drop primary key drop index;
(Optional) Rename the index:
alter index new_pk rename to c_name;
And then add the PK again indicating the index to be used:
alter table <tabname> add constraint c_name
primary key (column_2) using index c_name;

I don't know if this is a similar problem but, in DB2, you have to actually commit following the alter table statement. Otherwise it's still hanging around.