Thread: SQL CASE Statements
In the following CASE statement, is it possible to put a SELECT ... WHERE
EXISTS
in the <condition> of a CASE statement, and have it work?
The <condition> I want to do is to yield a result of '1' if the statement
finds
the value 'a' in a table (EXISTS evaluates true), and '0' if it evaluates
false
('a' not found).
SELECT a, CASE WHEN <CONDITION> THEN 1 ELSE 0 END
Has anybody done this? If so, can you send me a sample?
I am not sure what you are asking...
SELECT CASE WHEN EXISTS (SELECT foo FROM bar WHERE baz = 'a') THEN 1
ELSE 0 END;
Or
SELECT CASE WHEN 'a' = ANY (SELECT froo FROM bar) THEN 1 ELSE 0 END;
Both work, but that's pretty much what you had already - am I missing
what you are trying to achieve?
Though both are likely to be quite inefficient if you are looking up
many values.
Maybe something like:
SELECT f.a, CASE WHEN b.a IS NOT NULL THEN 1 ELSE 0 END
FROM foo f LEFT JOIN bar b USING (a)
Assuming "foo" has the values you want to look up, and "bar" is the
table you check for existence.
Dmitri
> -----Original Message-----
> From: pgsql-sql-owner@postgresql.org
> [mailto:pgsql-sql-owner@postgresql.org] On Behalf Of Lane Van Ingen
> Sent: Thursday, August 18, 2005 9:32 PM
> To: pgsql-sql@postgresql.org
> Subject: [SQL] SQL CASE Statements
>
>
> In the following CASE statement, is it possible to put a
> SELECT ... WHERE EXISTS in the <condition> of a CASE
> statement, and have it work?
>
> The <condition> I want to do is to yield a result of '1' if
> the statement finds the value 'a' in a table (EXISTS
> evaluates true), and '0' if it evaluates false ('a' not found).
>
> SELECT a,
> CASE WHEN <CONDITION> THEN 1
> ELSE 0
> END
>
> Has anybody done this? If so, can you send me a sample?
>
>
>
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> Has anybody done this? If so, can you send me a sample? CREATE TEMPORARY TABLE fruits (id SERIAL, name TEXT); INSERT INTO fruits VALUES (DEFAULT, 'banana'); INSERT INTO fruits VALUES (DEFAULT, 'apple'); CREATE TEMPORARY TABLE food (id SERIAL, name TEXT); INSERT INTO food VALUES (DEFAULT, 'apple'); INSERT INTO food VALUES (DEFAULT, 'spinach'); SELECT name, CASE WHEN name = ANY (SELECT name FROM fruits) THEN 'yes' ELSE 'no' END AS fruit FROM food; name | fruit ---------+-------apple | yesspinach | no (2 lines) __________________________________________________ Converse com seus amigos em tempo real com o Yahoo! Messenger http://br.download.yahoo.com/messenger/
Halley, here is a sample for you that might help; the purpose of this function was to set an indicator of '1' or '0' (true or false) on a router interface if the router interface ID was the same as the default gateway for the Router node ID: create view current_default_gateways_v (router_id, default_gateway) AS select router_id, case when router_id in (selectinterface_id from router_interface ri, network_nodes nn where ri.node_id = nn.node_id and ri.interface_id = nn.default_gateway_interface_id) then 1 else 0 end as if_default_gateway from router_interface; TABLES USED: network_nodes: node_id, serial node_name, varchar default_gateway_interface_id, integer router_interfaces: interface_id, serial (integer) node_id (FK) -----Original Message----- From: Halley Pacheco de Oliveira [mailto:halleypo@yahoo.com.br] Sent: Saturday, August 20, 2005 7:25 AM To: pgsql-sql@postgresql.org Cc: lvaningen@esncc.com Subject: RE: SQL CASE Statements > Has anybody done this? If so, can you send me a sample? CREATE TEMPORARY TABLE fruits (id SERIAL, name TEXT); INSERT INTO fruits VALUES (DEFAULT, 'banana'); INSERT INTO fruits VALUES (DEFAULT, 'apple'); CREATE TEMPORARY TABLE food (id SERIAL, name TEXT); INSERT INTO food VALUES (DEFAULT, 'apple'); INSERT INTO food VALUES (DEFAULT, 'spinach'); SELECT name, CASE WHEN name = ANY (SELECT name FROM fruits) THEN 'yes' ELSE 'no' END AS fruit FROM food; name | fruit ---------+-------apple | yesspinach | no (2 lines) __________________________________________________ Converse com seus amigos em tempo real com o Yahoo! Messenger http://br.download.yahoo.com/messenger/
Dear Lane, is that what you want?
CREATE TABLE network_nodes ( node_id SERIAL PRIMARY KEY, node_name VARCHAR, default_gateway_interface_id
INTEGER
);
CREATE TABLE router_interfaces ( interface_id SERIAL PRIMARY KEY, node_id INT REFERENCES network_nodes
);
CREATE VIEW current_default_gateways_v (router_id, default_gateway) AS SELECT interface_id, CASE WHEN
interface_idIN (SELECT interface_id FROM router_interfaces ri, network_nodes nn
WHERE ri.node_id = nn.node_id AND ri.interface_id = nn.default_gateway_interface_id) THEN
1 ELSE 0 END AS if_default_gateway FROM router_interfaces;
INSERT INTO network_nodes VALUES(DEFAULT, 'node1',1);
INSERT INTO network_nodes VALUES(DEFAULT, 'node2',2);
INSERT INTO network_nodes VALUES(DEFAULT, 'node3',3);
INSERT INTO network_nodes VALUES(DEFAULT, 'node4',4);
INSERT INTO router_interfaces VALUES(DEFAULT,1);
INSERT INTO router_interfaces VALUES(DEFAULT,2);
INSERT INTO router_interfaces VALUES(DEFAULT,2);
INSERT INTO router_interfaces VALUES(DEFAULT,1);
SELECT * FROM network_nodes;
SELECT * FROM router_interfaces;
SELECT * FROM current_default_gateways_v;
teste=> SELECT * FROM network_nodes;node_id | node_name | default_gateway_interface_id
---------+-----------+------------------------------ 1 | node1 | 1 2 | node2
| 2 3 | node3 | 3 4 | node4 |
4
(4 rows)
teste=> SELECT * FROM router_interfaces;interface_id | node_id
--------------+--------- 1 | 1 2 | 2 3 | 2 4 | 1
(4 rows)
teste=> SELECT * FROM current_default_gateways_v;router_id | default_gateway
-----------+----------------- 1 | 1 2 | 1 3 | 0 4
| 0
(4 rows)
--- Lane Van Ingen <lvaningen@esncc.com> escreveu:
> Halley, here is a sample for you that might help; the purpose of this
> function was to set an indicator of '1' or '0' (true or false) on a router
> interface if the router interface ID was the same as the default gateway for
> the Router node ID:
>
> create view current_default_gateways_v (router_id, default_gateway) AS
> select router_id,
> case
> when router_id in (select interface_id from router_interface ri,
> network_nodes nn
> where ri.node_id = nn.node_id
> and ri.interface_id = nn.default_gateway_interface_id)
> then 1
> else 0
> end as if_default_gateway
> from router_interface;
>
> TABLES USED:
> network_nodes:
> node_id, serial
> node_name, varchar
> default_gateway_interface_id, integer
>
> router_interfaces:
> interface_id, serial (integer)
> node_id (FK)
>
__________________________________________________
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