mysql add condition for derived max function column

Question

I have the following sql which is not working on the where condition.

SELECT t.PROJID,sum(t.UNITS) AS totalunits, sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` 
left join projects on projects.PROJID = t.PROJID 
where lastupdated LIKE '%2014-06-11%' 
GROUP BY t.PROJID

Answer 1

You should not use like on dates. The right solution is to simply truncate the date and do the comparison. However, you need to use the field in the data:

SELECT t.PROJID, sum(t.UNITS) AS totalunits,
       sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join
     projects on projects.PROJID = t.PROJID 
where date(t.date) = date('2014-06-11')
GROUP BY t.PROJID;

Or, if you have an index on lastupdated , using a range allows the use of the index:

SELECT t.PROJID, sum(t.UNITS) AS totalunits,
       sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join
     projects on projects.PROJID = t.PROJID 
where t.date >= date('2014-06-11') and t.date < date('2014-06-12')
GROUP BY t.PROJID;

You might really be wanting to use having , which is suggested by the use of the column alias instead of the base column. In that case:

SELECT t.PROJID, sum(t.UNITS) AS totalunits,
       sum(t.COST) AS totalcost, project, max(t.DATE) as lastupdated, PROJCODE 
FROM `projectcosts` `t` left join
     projects on projects.PROJID = t.PROJID 
GROUP BY t.PROJID
HAVING date(lastupdated) = date('2014-06-11');

Answer 2

Like can never be used with date field. If you are changing the type to vachar it is possible