Select Case inside another Select - mysql

Question

I’m trying to apply a CASE to a column that I create.
But the problem is that I have a select inside another select
And I’m using the value of that subquery to make the select case
How should I do this?
SELECT
gc.IDGastosComunes,
v.IDPropiedad,
v.Depto,
v.NombreDueno,
(SELECT u2.IDCategoria
FROM usuarios_tipos u2
WHERE u2.IDUsuario = v.IDDueno AND
u2.IDTipo = 10) AS gc.IDCategoria, <-- This return an int -> 1, 2 or 3
CASE
WHEN IDCategoria = 1 THEN 'Convenio'
WHEN IDCategoria = 2 THEN 'Plus'
WHEN IDCategoria = 3 THEN 'Preferente'
WHEN IDCategoria = 4 THEN 'Premium'
WHEN IDCategoria = 5 THEN 'La Serena'
ELSE ''
END AS Categoria, <-- This has to show the string
gc.monto,
gc.FechaEmisionPago AS Periodo
FROM
gastos_comunes gc
JOIN vcartera_propiedades v ON (v.IDPropiedad=gc.IDPropiedad)
WHERE v.IDGrupo = 1

Answer 1

You would typically move the case expression inside the subquery:
SELECT
gc.IDGastosComunes,
v.IDPropiedad,
v.Depto,
v.NombreDueno,
(
SELECT CASE u2.IDCategoria
WHEN 1 THEN 'Convenio'
WHEN 2 THEN 'Plus'
WHEN 3 THEN 'Preferente'
WHEN 4 THEN 'Premium'
WHEN 5 THEN 'La Serena'
ELSE ''
END
FROM usuarios_tipos u2
WHERE u2.IDUsuario = v.IDDueno AND u2.IDTipo = 10
) AS Categoria
gc.monto,
gc.FechaEmisionPago AS Periodo
FROM gastos_comunes gc
JOIN vcartera_propiedades v ON v.IDPropiedad=gc.IDPropiedad
WHERE v.IDGrupo = 1
Side note: this would need to be tested, but likely, your query can be rewritten to use a (LEFT) JOIN instead of an inline subquery, which would make the syntax much shorter. That would look like:
SELECT
gc.IDGastosComunes,
v.IDPropiedad,
v.Depto,
v.NombreDueno,
CASE u2.IDCategoria
WHEN 1 THEN 'Convenio'
WHEN 2 THEN 'Plus'
WHEN 3 THEN 'Preferente'
WHEN 4 THEN 'Premium'
WHEN 5 THEN 'La Serena'
ELSE ''
END AS Categoria
gc.monto,
gc.FechaEmisionPago AS Periodo
FROM gastos_comunes gc
JOIN vcartera_propiedades v ON v.IDPropiedad=gc.IDPropiedad
LEFT JOIN usuarios_tipos u2 ON u2.IDUsuario = v.IDDueno AND u2.IDTipo = 10
WHERE v.IDGrupo = 1