Sql-server – PostgreSQL and/or SQL Server alternatives to Oracle’s SYS_CONTEXT

oraclepostgresqlsql-server

Having used an Oracle DB for a while, I got used to using the Oracle DB Application Context to implement access restrictions. To simply put it, upon login a procedure is called that puts the user details into the Oracle Application context like so:

DBMS_SESSION.SET_CONTEXT('context_name', 'user_id', user_id);

Then access can be enforced by creating views that would look in the context to determine which rows can be seen by a user like so:

CREATE VIEW users_vw AS 
SELECT *
  FROM users
 WHERE user_id = SYS_CONTEXT('context_name', 'user_id');

I have now moved away from Oracle and am using PostgreSQL for personal projects and SQL Server 2000 and 2008 at work. Can anyone tell me if there are corresponding capabilities that PostgreSQL or SQL Server offer?

Best Solution

In PostgreSQL, you could perhaps get by with SECURITY DEFINER-functions that reason on the current user? Documented here: http://www.postgresql.org/docs/8.4/static/sql-createfunction.html

Edit:

plperl can be used for session variables. There are other alternatives (see link in comment), but plperl is the simplest of them.

Syntax:

ALTER TABLE {TABLENAME} 
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL} 
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES

Example:

ALTER TABLE SomeTable
        ADD SomeCol Bit NULL --Or NOT NULL.
 CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
    DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.

Notes:

Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6

Optional With-Values Statement:
The WITH VALUES is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES or not.

How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable and do not Specify SomeCol's value, then it will Default to 0.
If you insert a Record and Specify SomeCol's value as NULL (and your column allows nulls),
then the Default-Constraint will not be used and NULL will be inserted as the Value.

Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.

PostgreSQL “DESCRIBE TABLE”

Try this (in the psql command-line tool):

\d+ tablename

See the manual for more info.

Best Solution

Related Solutions

Sql – Add a column with a default value to an existing table in SQL Server

Syntax:

Example:

Notes:

PostgreSQL “DESCRIBE TABLE”

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