mysql - What's wrong with given query regarding displaying ad counters for categories? -


i have asp.net website users can put ads. in there want display ad counters each category. using mysql db.

to using query

    select      type.`type_id_pk`,     type.`name`,     count(head.`header_id_pk`) `count`        `testdb`.`type` `type`      left join `header` head        on head.`type_id_fk` = type.`type_id_pk`    group type.`type_id_pk`    order `name` asc ;

above query works fine. in site separate ads in countries. want display ad counters country. modified above query this

        select          type.`type_id_pk`,         type.`name`,         count(head.`header_id_pk`) `count`                `testdb`.`type` `type`          left join `header` head            on head.`type_id_fk` = type.`type_id_pk`    head.`country_id_fk` = _country_id        group type.`type_id_pk`        order `name` asc ;

_country_id place insert specific country id. above query returns rows have ads. if there no ad category not displaying. so want display categories along counters specific country.( including 0 ad categories) .so whats wrong above query? ( please consider query efficiency. )

essentially code seems enforce inner join, null results excluded. might try left outer join include null results, , lighten restriction in where clause weeds out null results.

        left outer join `header` head            on head.`type_id_fk` = type.`type_id_pk`    head.`country_id_fk` = _country_id or head.`country_id_fk` null

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