Where clause for only one table in a left join

Question

I have two tables, the first is \'actions\' which has columns \'id\' and \'actionname\', the second is \'completedactions\' which has \'userid\' and \'actionid\'. They look

Answer 1

select 
  actions.id, 
  actions.actionname, 
  count(completedactions.actionid) 
from actions
left join completedactions 
  on completedactions.actionid = actions.id and completedactions.userid = 1
group by 1,2

Answer 2

select * from actions

left outer join completedactions on ( completedactions.actionid = actions.id and completedactions.userid=1 )

Answer 3

its will be help full if any body have need to use it.

select `m`.`id` AS `id`,
`m`.`CategoryParentId` AS `CategoryParentId`,
`m`.`CategoryChildId` AS `CategoryChildId`,
`p`.`CategoryName` AS `ParentCategory`,
`c`.`CategoryName` AS `ChildCategory`,
count(c_p.category_id) AS `prodcuts`,
`img`.`image` AS `CategoryImage`,
`img2`.`image` AS `thumbImage`
from (((((`tblcategoryparentchildassociations` `m` 
    left join `tblmastercategories` `c` on((`c`.`id` =  `m`.`CategoryChildId`))) 
    left join `tblmastercategories` `p` on((`p`.`id` = `m`.`CategoryParentId`)))
    left join `vwimagetypeassociations` `img` on((`c`.`id` = `img`.`domainid` AND `img`.`imagetypeid` = 2 AND `img`.`status` = 1 )))
    left join `vwimagetypeassociations` `img2` on((`c`.`id`= `img`.`domainid`AND `img2`.`imagetypeid` = 3 AND `img`.`status` = 1)))
    left join `tblproductcategoriesassociations` `c_p` on((`m`.`CategoryChildId` = `c_p`.`category_id`)))
group by m.id

Answer 4

Try using your WHERE condition in your ON() clause instead, i.e., ON (c.actionid = a.id AND c.user_id = 1).

The WHERE filter will apply on the whole resultset, while an additional condition in the join will join the matched results and give null for non-matched results.

SELECT a.*,c.user_id FROM 
actions a 
LEFT JOIN completedactions c 
ON (c.actionid = a.id AND c.user_id = 1)