Re: Select in From clause - Mailing list pgsql-sql

From Bart Degryse
Subject Re: Select in From clause
Date
Msg-id 47381B85.A3DD.0030.0@indicator.be
Whole thread Raw
In response to Select in From clause  ("Ray Madigan" <ray@madigans.org>)
List pgsql-sql
Consider this:
CREATE TABLE "public"."test" (
  "id" INTEGER NOT NULL,
  "tbl" TEXT
) WITHOUT OIDS;

INSERT INTO "public"."test" ("id", "tbl") VALUES (1, 'status');
INSERT INTO "public"."test" ("id", "tbl") VALUES (2, 'yearplan');
 
Following two statements will return one record.
select tbl from test where id = 1
select * from (select tbl from test where id = 1) a
 
tbl
status
 
Following statement will return all records from table 'test' where the 'tbl' field contains a 'y'.
select * from (select tbl from test) a where a.tbl like '%y%'
tbl
yearplan
 
So it does work. Just change you statement to something like:
SELECT * FROM (SELECT name, condition FROM bar WHERE conditions) AS b WHERE b.condition = xxx;
or
SELECT * FROM (SELECT name FROM bar WHERE conditions) AS b WHERE b.name = xxx;


>>> "Ray Madigan" <ray@madigans.org> 2007-11-09 18:21 >>>
I have never seen this done before, but it seems like it is supposed to work
from reading the manual.

I want to be able to get a table name from another table and use it in the
from clause of a select.

Something like

SELECT * FROM (SELECT name FROM bar WHERE conditions) AS b WHERE b.condition
= xxx;

which translates to something like

SELECT * FROM Dealer AS b WHERE b.zipcode = 12345;

The translated version works but the SELECT in FROM version reports that
b.condition does not exist.


---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

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