Обсуждение: Return LEFT JOINed tables when one has no matching column
Hi all, I've got a variation on a question I asked some time ago... I've got a table that is simply a collection of "variable" -> "value" columns with a pointer to another table. I use this as little as possible, given how much of a headache it is, but I've run into a situation where I need to pull something from it in a JOIN query. Trick is, the column 'variable' may simply not exist, but I want the rest of the query to return and let it be NULL. Specifically, I've got a query like this: SELECT a.tbl1_name, b.tbl2_date, c.tbl3_value AS some_value FROM table_1 a LEFT JOIN table_2 b ON (a.tbl1_id=b.tbl2_tbl1_id) LEFT JOIN table_3 c ON (a.tbl1_id=c.tbl3_tbl1_id) WHERE c.tbl3_variable='some_variable' AND a.tbl1_id=123; I want the data from table_1 and table_2 to return and table_3 to return NULL when there is no matching c.tbl3_variable='some_variable'. Is this possible? Thanks as always! Madi
In article <4A425379.90907@alteeve.com>, Madison Kelly <linux@alteeve.com> writes: > SELECT > a.tbl1_name, > b.tbl2_date, > c.tbl3_value AS some_value > FROM > table_1 a > LEFT JOIN > table_2 b ON (a.tbl1_id=b.tbl2_tbl1_id) > LEFT JOIN > table_3 c ON (a.tbl1_id=c.tbl3_tbl1_id) > WHERE > c.tbl3_variable='some_variable' > AND > a.tbl1_id=123; > I want the data from table_1 and table_2 to return and table_3 to > return NULL when there is no matching > c.tbl3_variable='some_variable'. Is this possible? Move "c.tbl3_variable='some_variable'" from WHERE to c's ON clause.
Harald Fuchs wrote: > In article <4A425379.90907@alteeve.com>, > Madison Kelly <linux@alteeve.com> writes: > >> SELECT >> a.tbl1_name, >> b.tbl2_date, >> c.tbl3_value AS some_value >> FROM >> table_1 a >> LEFT JOIN >> table_2 b ON (a.tbl1_id=b.tbl2_tbl1_id) >> LEFT JOIN >> table_3 c ON (a.tbl1_id=c.tbl3_tbl1_id) >> WHERE >> c.tbl3_variable='some_variable' >> AND >> a.tbl1_id=123; > >> I want the data from table_1 and table_2 to return and table_3 to >> return NULL when there is no matching >> c.tbl3_variable='some_variable'. Is this possible? > > Move "c.tbl3_variable='some_variable'" from WHERE to c's ON clause. Bingo, thank you! Madi