Tim,
Tuesday, February 26, 2002, 4:20:46 AM, you wrote:
TP> Hi,
TP> I am trying to make a database-neutral application.
TP> What is the MySQL idiom to replace the Postgres EXISTS function?
TP> I have two tables:
TP> mysql> select * from groupcapability;
TP> +----+--------------+------------+
TP> | id | melati_group | capability |
TP> +----+--------------+------------+
TP> | 0 | 0 | 0 |
TP> +----+--------------+------------+
TP> mysql> select * from groupmembership;
TP> +----+------+--------------+
TP> | id | user | melati_group |
TP> +----+------+--------------+
TP> | 0 | 1 | 0 |
TP> +----+------+--------------+
TP> In Postgres the following query works:
TP> SELECT * FROM groupmembership WHERE "user" = 1 AND
TP> EXISTS (
TP> SELECT groupcapability."melati_group" , capability
TP> FROM groupcapability, groupmembership
TP> WHERE
TP> groupcapability."melati_group" = groupmembership."melati_group"
TP> AND
TP> capability = 0 );
TP> How should this be written in MySQL?
TP> (NB I have had to use melati_group instead of group due to MySQL objecting to
TP> the keyword group.)
MySQL currently doesn't support sub-selects.
Take a look at JOIN statement and a temporary tables usage.
You can find info about it in the manual:
http://www.mysql.com/doc/J/O/JOIN.html
http://www.mysql.com/doc/A/N/ANSI_diff_Sub-selects.html
http://www.mysql.com/doc/C/R/CREATE_TABLE.html
TP> tia
TP> timp
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