Left join with dynamic table name retrieved from column

Question

I'm new to PostgreSQL, and I'm wondering if it can be used numberfrom a table tbcas part of the table name in the left join 'pa' || number. So, for example, if the number is 456887, I want the left join with the pa456887 table. Something like that:

SELECT tdc.cpa, substring(tdc.ku,'[0-9]+') AS number, paTab.vym 
FROM public."table_data_C" AS tdc
LEFT JOIN concat('pa' || number) AS paTab ON (paTab.cpa = tdc.cpa)

And I want to use only PostgreSQL, and not additional code in PHP, for example.

Answer 1

In any case, you need dynamic SQL.

Table name as a given parameter

CREATE OR REPLACE FUNCTION foo(_number int)
  RETURNS TABLE (cpa int, nr text, vym text) AS  -- adapt to actual data types!
$func$
BEGIN
   RETURN QUERY EXECUTE format(
      'SELECT t.cpa, substring(t.ku,'[0-9]+'), p.vym 
       FROM   public."table_data_C" t
       LEFT   JOIN %s p USING (cpa)'
     , 'pa' || _number
     );
END
$func$ LANGUAGE plpgsql;

Call:

SELECT * FROM foo(456887)

, format ( %I ), SQL. integer , . :
INSERT

. / ...
, number as. SQL.

. tableoid :

SELECT * FROM parent_table
WHERE  tableoid = 'pa456887'::regclass

, . :

• ,
• () , Postgres

2- 1-

.

LEFT JOIN tableoid. , COALESCE.

SELECT t.*, t.tbl, COALESCE(p1.vym, p2.vym, p3.vym) AS vym
FROM  (
   SELECT cpa, ('pa' || substring(ku,'[0-9]+'))::regclass AS tbl
   FROM   public."table_data_C"
   -- WHERE <some condition>
   ) t
LEFT   JOIN pa456887 p1 ON p1.cpa = t.cpa AND p1.tableoid = t.tbl
LEFT   JOIN pa456888 p2 ON p2.cpa = t.cpa AND p2.tableoid = t.tbl
LEFT   JOIN pa456889 p3 ON p3.cpa = t.cpa AND p3.tableoid = t.tbl

:

CREATE OR REPLACE FUNCTION foo(_number int)
  RETURNS TABLE (cpa int, nr text, vym text) AS
$func$
DECLARE
   _nr text;
BEGIN
FOR _nr IN
   SELECT DISTINCT substring(ku,'[0-9]+')
   FROM   public."table_data_C"
LOOP
   RETURN QUERY EXECUTE format(
      'SELECT t.cpa, _nr, p.vym 
       FROM   public."table_data_C" t
       LEFT   JOIN %I p USING (cpa)
       WHERE  t.ku LIKE (_nr || '%')'
     , 'pa' || _nr
     );
END LOOP;

END
$func$ LANGUAGE plpgsql;