Re: [HACKERS] proposal: schema variables

> Hi,
> 
> I propose a  new database object - a variable. The variable is persistent
> object, that holds unshared session based not transactional in memory value
> of any type. Like variables in any other languages. The persistence is
> required for possibility to do static checks, but can be limited to session
> - the variables can be temporal.
> 
> My proposal is related to session variables from Sybase, MSSQL or MySQL
> (based on prefix usage @ or @@), or package variables from Oracle (access
> is controlled by scope), or schema variables from DB2. Any design is coming
> from different sources, traditions and has some advantages or
> disadvantages. The base of my proposal is usage schema variables as session
> variables for stored procedures. It should to help to people who try to
> port complex projects to PostgreSQL from other databases.
> 
> The Sybase  (T-SQL) design is good for interactive work, but it is weak for
> usage in stored procedures - the static check is not possible. Is not
> possible to set some access rights on variables.
> 
> The ADA design (used on Oracle) based on scope is great, but our
> environment is not nested. And we should to support other PL than PLpgSQL
> more strongly.
> 
> There is not too much other possibilities - the variable that should be
> accessed from different PL, different procedures (in time) should to live
> somewhere over PL, and there is the schema only.
> 
> The variable can be created by CREATE statement:
> 
> CREATE VARIABLE public.myvar AS integer;
> CREATE VARIABLE myschema.myvar AS mytype;
> 
> CREATE [TEMP] VARIABLE [IF NOT EXISTS] name AS type
>   [ DEFAULT expression ] [[NOT] NULL]
>   [ ON TRANSACTION END { RESET | DROP } ]
>   [ { VOLATILE | STABLE } ];
> 
> It is dropped by command DROP VARIABLE  [ IF EXISTS] varname.
> 
> The access rights is controlled by usual access rights - by commands
> GRANT/REVOKE. The possible rights are: READ, WRITE
> 
> The variables can be modified by SQL command SET (this is taken from
> standard, and it natural)
> 
> SET varname = expression;
> 
> Unfortunately we use the SET command for different purpose. But I am
> thinking so we can solve it with few tricks. The first is moving our GUC to
> pg_catalog schema. We can control the strictness of SET command. In one
> variant, we can detect custom GUC and allow it, in another we can disallow
> a custom GUC and allow only schema variables. A new command LET can be
> alternative.
> 
> The variables should be used in queries implicitly (without JOIN)
> 
> SELECT varname;
> 
> The SEARCH_PATH is used, when varname is located. The variables can be used
> everywhere where query parameters are allowed.
> 
> I hope so this proposal is good enough and simple.
> 
> Comments, notes?

Just q quick follow up. Looks like a greate feature!

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp


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