Mysql COUNT (*) en múltiples mesas

Question

¿Qué hay de malo en esta consulta:

SELECT co.*, mod.COUNT(*) as moduleCount, vid.COUNT(*) as vidCount 
FROM courses as co, modules as mod, videos as vid 
WHERE mod.course_id=co.id AND vid.course_id=co.id ORDER BY co.id DESC 

En otras palabras, ¿cómo lo puedo hacer lo mismo con cada registro regresó de 'cursos', hay una columna adicional llamada ' modCount 'que muestra el número de registros en la tabla de módulos para ese curso_id, y otro llamado' vidCount 'que hace lo mismo para la tabla de videos.

error:

Error Number: 1064

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') as moduleCount, vid.COUNT() as vidCount FROM courses as co, ' at line 1

Answer 1

usando subselects que puede hacer:

SELECT co.*, 
    (SELECT COUNT(*) FROM modules mod WHERE mod.course_id=co.id) AS moduleCount, 
    (SELECT COUNT(*) FROM videos vid WHERE vid.course_id=co.id) AS vidCount 
FROM courses AS co 
ORDER BY co.id DESC 

Pero tenga cuidado, ya que es una consulta de cursos caros cuando tiene muchas filas.

EDIT: Si las tablas son bastante grandes la siguiente consulta debe realizar mucho mejor (a favor de ser más compleja de leer y entender).

SELECT co.*, 
    COALESCE(mod.moduleCount,0) AS moduleCount, 
    COALESCE(vid.vidCount,0) AS vidCount 
FROM courses AS co 
    LEFT JOIN (
      SELECT COUNT(*) AS moduleCount, course_id AS courseId 
      FROM modules 
      GROUP BY course_id 
     ) AS mod 
     ON mod.courseId = co.id 
    LEFT JOIN (
      SELECT COUNT(*) AS vidCount, course_id AS courseId 
      FROM videos 
      GROUP BY course_id 
     ) AS vid 
     ON vid.courseId = co.id 
ORDER BY co.id DESC 

Answer 2

SELECT co.*, 
     (
     SELECT COUNT(*) 
     FROM modules mod 
     WHERE mod.course_id = co.id 
     ) AS modCount, 
     (
     SELECT COUNT(*) 
     FROM videos vid 
     WHERE vid.course_id = co.id 
     ) AS vidCount 
FROM courses co 
ORDER BY 
     co.id DESC 

Answer 3

SELECT co.*, m.ModCnt as moduleCount, v.VidCnt as vidCount 
FROM courses co 
INNER JOIN (
     select count(*) AS ModCnt, co.id AS CoID 
     from modules 
     group by co) m 
    ON m.CoID = co.id 
INNER JOIN (
     select count(*) AS VidCnt, co.id AS CoID 
     from videos 
     group by co) v 
    ON v.CoID = co.id 
INNER JOIN videos vid 
    ON vid.course_id = co.id 
ORDER BY co.id DESC 

Answer 4

Dispara esto. Me hizo el trabajo con algo de código no mysql:

function getAllWithStats($info='*',$order='',$id=0) 
{ 
    $courses=$this->getAll($info,$order,$id); 

    foreach ($courses as $k=>$v) 
    { 
     $courses[$k]['modCount']=$this->getModuleCount($v['id']); 
     $courses[$k]['vidCount']=$this->getVideoCount($v['id']); 
    } 

    return $courses; 
} 

Answer 5

tengo solución mejor y fácil

SELECT COUNT(*),(SELECT COUNT(*) FROM table2) FROM table1