PSQL/SQL constraint to insert or delete - sql

Question

I have these tables:
user
id
permission
id
user_id
old_permission
user_id
value
Values:
user
id
1
2
3
permission
id user_id
1 1
2 2
old_permission
user_id value
1 f
2 f
3 t
As the table names suggest, I am migrating from a legacy permissions system. What I want to do is:
When old_permission.value is 't', i want any matching rows in permission for the user to be deleted. So if user 3 had an entry in the permission table, it would be deleted if its old_permission.value = 't'.
I also want to create a row in the permission table if the associated old_permission.value = 'f'
How can I create a constraint like this?

Answer 1

I would create a Stored Procedure that refreshes the Permission table based on the Old_Permission table:
CREATE PROCEDURE RefreshPermissions()
AS
BEGIN
DELETE
Permission
WHERE
EXISTS
(SELECT
NULL
FROM
Old_Permission
WHERE
Permission.user_id = Old_Permission.user_id
AND Old_Permission.Value = 't');
INSERT INTO
Permission (user_id)
SELECT
Old_Permission.user_id
FROM
Old_Permission
LEFT JOIN Permission ON Old_Permission.user_id = Permission.user_id
WHERE
Old_Permission.Value = 'f'
AND Permission.user_Id IS NULL;
END;
Then I would suggest using triggers on the Old_Permission table to modify the Permission table as needed. Something like this:
CREATE TRIGGER
TR_Old_Permission
AFTER INSERT OR UPDATE OR DELETE ON
Old_Permission
EXECUTE PROCEDURE
RefreshPermissions();

Answer 2

The PL/SQL is part of Oracle. And Constraints are part of SQL not PL/SQL. You cannot create constraints like this. You need to write some code, could be procedures and/or triggers that would delete and insert according to your logic. Basically, while migrating, and I do not know what exactly you are doing to migrate and how, you loop through records then delete and insert records according to your conditions/filters. It is hard to suggest anything more as I need more details to decide how and what to do exactly in your case.

Answer 3

i am not able to understand the exact problem of yours,for that i thought of making u to understand the concept of the constraints in sql,including its defination and types.
Constraints are used to limit the type of data that can go into a table.
Constraints can be specified when a table is created (with the CREATE TABLE statement) or after the table is created (with the ALTER TABLE statement).
types of constraints:
•NOT NULL
•UNIQUE
•PRIMARY KEY
•FOREIGN KEY
•CHECK
•DEFAULT
Explanitation of the types of constraints with small examples for each:-
SQL NOT NULL Constraint
•The NOT NULL constraint enforces a column to NOT accept NULL values.
•The NOT NULL constraint enforces a field to always contain a value. This means that you
cannot insert a new record, or update a record without adding a value to this field.
•The following SQL enforces the "P_Id" column and the "LastName" column to not accept NULL
values:
•CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
SQL UNIQUE Constraint
The UNIQUE constraint uniquely identifies each record in a database table.
SQL UNIQUE Constraint on CREATE TABLE
The following SQL creates a UNIQUE constraint on the "P_Id" column when the "Persons" table
is created:
MySQL:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
UNIQUE (P_Id)
)
SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL UNIQUE,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
To allow naming of a UNIQUE constraint, and for defining a UNIQUE constraint on multiple
columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)
)
SQL UNIQUE Constraint on ALTER TABLE
To create a UNIQUE constraint on the "P_Id" column when the table is already created,
use the following SQL:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD UNIQUE (P_Id)
To allow naming of a UNIQUE constraint, and for defining a UNIQUE constraint on multiple
columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD CONSTRAINT uc_PersonID UNIQUE (P_Id,LastName)
To DROP a UNIQUE Constraint
To drop a UNIQUE constraint, use the following SQL:
MySQL:
ALTER TABLE Persons
DROP INDEX uc_PersonID
SQL Server / Oracle / MS Access:
ALTER TABLE Persons
DROP CONSTRAINT uc_PersonID
SQL PRIMARY KEY Constraint
The PRIMARY KEY constraint uniquely identifies each record in a database table.
Primary keys must contain unique values.
A primary key column cannot contain NULL values.
Each table should have a primary key, and each table can have only ONE primary key.
SQL PRIMARY KEY Constraint on CREATE TABLE
The following SQL creates a PRIMARY KEY on the "P_Id" column when the "Persons" table is
created:
MySQL:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
PRIMARY KEY (P_Id)
)
SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on
multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)
)
SQL FOREIGN KEY Constraint on CREATE TABLE
The following SQL creates a FOREIGN KEY on the "P_Id" column when the "Orders" table is
created:
MySQL:
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(P_Id)
)
SQL Server / Oracle / MS Access:
CREATE TABLE Orders
(
O_Id int NOT NULL PRIMARY KEY,
OrderNo int NOT NULL,
P_Id int FOREIGN KEY REFERENCES Persons(P_Id)
)
To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on
multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
CONSTRAINT fk_PerOrders FOREIGN KEY (P_Id)
REFERENCES Persons(P_Id)
)
SQL CHECK Constraint on CREATE TABLE
The following SQL creates a CHECK constraint on the "P_Id" column when the "Persons" table
is created. The CHECK constraint specifies that the column "P_Id" must only include integers greater than 0.
MySQL:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CHECK (P_Id>0)
)
SQL DEFAULT Constraint
The DEFAULT constraint is used to insert a default value into a column.
SQL DEFAULT Constraint on CREATE TABLE
The following SQL creates a DEFAULT constraint on the "City" column when the "Persons"
table is created:
My SQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255) DEFAULT 'Sandnes'
)
The DEFAULT constraint can also be used to insert system values, by using functions like
GETDATE():
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
OrderDate date DEFAULT GETDATE()
)
above explination is in general format of using constraints,hope it may help you to overcome from your problem...........................