Re: checking if sequence exists

[Bob Lunney <bob_lunney@xxxxxxxxx>]

Thara,

Here are your functions:

bob=> create sequence foo;

CREATE SEQUENCE

bob=> create or replace function public.chk_sequence(namespace name, seq_name name)

bob->  returns int

bob->  language sql

bob-> as $$

bob$>   select count(*)::int as sequence_exists

bob$>     from pg_class c, pg_namespace n

bob$>    where c.relnamespace = n.oid

bob$>      and c.relkind in ('S', 's', '')

bob$>      and pg_table_is_visible(c.oid)

bob$>      and n.nspname = $1

bob$>      and c.relname = $2;

bob$> $$;

CREATE FUNCTION

bob=> select chk_sequence('public', 'foo');

 chk_sequence

--------------

            1

(1 row)

bob=> select chk_sequence('public', 'bar');

 chk_sequence

--------------

            0

(1 row)

bob=> ----

bob=> -- when you get tired of typing 'public' use this version

bob=> ----

bob=> create or replace function chk_sequence(seq_name name)

bob->   returns int

bob->   language sql

bob-> as $$

bob$>   select chk_sequence('public', $1);

bob$> $$;

CREATE FUNCTION

bob=> select chk_sequence('foo');

 chk_sequence

--------------

            1

(1 row)

bob=> select chk_sequence('bar');

 chk_sequence

--------------

            0

(1 row)

On Friday, November 15, 2013 5:39 PM, Thara Vadakkeveedu <tharagv@xxxxxxxxx> wrote:

By itself this sql works:

SELECT 0 FROM pg_class
             WHERE relkind = 'S'
               AND oid = ('public.' || quote_ident('hibernate_sequence'))::regclass;

 

However when I create a function for it and run it I see an error

 

create function chk_sequence() returns integer as $$
BEGIN
IF EXISTS (SELECT 1 FROM pg_class
             WHERE relkind = 'S'
             AND oid = ('public.' || quote_ident('hibernate_sequence')))::regclass

  THEN
        return 1;
  ELSE
 return 0;
    END IF;

END;
$$ language plpgsql;

 

 

select chk_sequence();
ERROR:  operator does not exist: oid = text
LINE 3:              AND oid = ('public.' || quote_ident('hibernate_...
                             ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
QUERY:  SELECT EXISTS (SELECT 1 FROM pg_class
             WHERE relkind = 'S'
             AND oid = ('public.' || quote_ident('hibernate_sequence')))::regclass

 

Thanks.

From: Elliot <yields.falsehood@xxxxxxxxx>
To: Thara Vadakkeveedu <tharagv@xxxxxxxxx>; Kevin Grittner <kgrittn@xxxxxxxxx>; "pgsql-admin@xxxxxxxxxxxxxx" <pgsql-admin@xxxxxxxxxxxxxx>
Sent: Friday, November 15, 2013 4:13 PM
Subject: Re: checking if sequence exists

On 2013-11-15 16:09, Thara Vadakkeveedu wrote:

"First, is this code in a plpgsql contex"?

 

No, that is my problem.

 

Does it have to be inside a Create function block or can just wrapping the if  with a BEGIN END; suffice ?

 

Control structures like if statements don't exist in straight sql - you need a procedural language like pl/pgsql for that. Wrapping sql statements in begin/end only affects the transactional context of the statements, it does not cause them to be interpreted as pl/pgsql. You can either create a function or you can use a "DO" block, which is sometimes what I use for deploy scripts [http://www.postgresql.org/docs/9.3/static/sql-do.html

].