How to Display a Field in the WHERE Clause with GROUP BY in MySQL?

SQL Query with WHERE Clause for Specific Field

Initial Problem:

In MySQL, you are unable to display a database table field's data in a query's WHERE clause when other fields not included in the WHERE clause are also present in the query's GROUP BY clause. Specifically:

<code class="sql">SELECT cursos.cursoID AS idcurso, cursos.estadoCurso,
cursosUsuarios.userHabilitado AS 'ok',                              
GROUP_CONCAT(cursosUsuarios.userID SEPARATOR ',') AS 'usuarios'
FROM cursos LEFT JOIN cursosUsuarios
ON cursos.cursoID = cursosUsuarios.cursoID
LEFT JOIN usuarios
ON cursosUsuarios.userID = usuarios.userID
WHERE cursos.estadoCurso='abierto'
GROUP BY cursos.cursoID;</code>

Proposed Solution:

Unfortunately, this limitation cannot be directly overcome within MySQL. However, there are alternative strategies to achieve the desired result:

Solution 1: Subquery

Create a subquery to retrieve the desired field data:

<code class="sql">SELECT userID, userHabilitado
FROM cursosUsuarios
WHERE userID = 70</code>

Then, join this subquery with the main query using the appropriate field(s):

<code class="sql">SELECT cursos.cursoID AS idcurso, cursos.estadoCurso,
(SELECT userHabilitado 
 FROM cursosUsuarios 
 WHERE userID = 70) AS 'userHabilitado',                              
GROUP_CONCAT(cursosUsuarios.userID SEPARATOR ',') AS 'usuarios'
FROM cursos LEFT JOIN cursosUsuarios
ON cursos.cursoID = cursosUsuarios.cursoID
LEFT JOIN usuarios
ON cursosUsuarios.userID = usuarios.userID
WHERE cursos.estadoCurso='abierto'
GROUP BY cursos.cursoID;</code>

Solution 2: Nested Query

Reformulate the query using a nested query:

<code class="sql">SELECT idcurso, estadoCurso, 'userHabilitado'
FROM (
  SELECT cursoID AS idcurso, estadoCurso, userHabilitado
  FROM cursos LEFT JOIN cursosUsuarios
  ON cursos.cursoID = cursosUsuarios.cursoID
  WHERE cursos.estadoCurso='abierto'
  GROUP BY cursoID
) AS subquery
WHERE userHabilitado = 1;</code>

Both these solutions allow you to display the userHabilitado field data for specific users in the WHERE clause while including other fields in the GROUP BY clause.

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