PostgreSQL: Create table if not exists AS

Question

I\'m using PostgreSQL and am an SQL beginner. I\'m trying to create a table from a query, and if I run:

CREATE TABLE table_name AS
   (....query...)
<         


        

Answer 1

If you are going to write a function for this, base it on system catalog table pg_class, not on views in the information schema or the statistics collector (which only exist if activated).

• How to check if a table exists in a given schema

CREATE OR REPLACE FUNCTION create_table_qry(_tbl text
                                          , _qry text
                                          , _schema text = NULL)
  RETURNS bool AS
$func$
DECLARE
  _sch text := COALESCE(_schema, current_schema());
BEGIN

IF EXISTS (
   SELECT 1 
   FROM   pg_catalog.pg_class c
   JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
   WHERE  n.nspname = _sch
   AND    c.relname = _tbl
   ) THEN

   RAISE NOTICE 'Name is not free: %.%',_sch, _tbl;
   RETURN  FALSE;
ELSE
EXECUTE format('CREATE TABLE %I.%I AS %s', _sch, _tbl, _qry);

   RAISE NOTICE 'Table created successfully: %.%',_sch, _tbl;
   RETURN  TRUE;
END IF;

END
$func$  LANGUAGE plpgsql;

The function takes a table name and the query string, and optionally also a schema to create the table in (defaults to the current schema).

Note the correct use of = in the function header and := in the function body:

• The forgotten assignment operator "=" and the commonplace ":="

Also note how identifiers are escaped as identifiers. You can't use regclass, since the table does not exist, yet:

• Table name as a PostgreSQL function parameter