Thread: Select in From clause
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.
Ray Madigan wrote: > 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; No, that's not how it works. The stuff returned by the inner select is a set of rows which can be further operated upon by the outer select. It is not expanded into a table name. One way to construct queries is to build plpgsql functions and use EXECUTE. However, the approach you are using looks like bad practice (read: bad database design). -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
Consider this:
CREATE TABLE "public"."test" (
"id" INTEGER NOT NULL,
"tbl" TEXT
) WITHOUT OIDS;
"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
>>> "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