Get column where relation is not NULL - mysql

Question

I have a database which was migrated from SQL Server to MySQL. I had an existing query in SQL Server to get the value of a column where the relation is not null, I mean, if the relation between two tables is null then it means that there should be a relation with another table.
This is the query I was using:
SELECT C.expediente,
C.status,
Sum(M.monto) AS monto,
Sum(M.interes) AS interes,
Sum(M.iva) AS iva,
Sum(M.capital) AS capital,
M.fecha_mov,
AB.tipo_abono,
AB.id_deposito,
Isnull(Min(tg.nombre), Min(tp.nombcomp)) AS nombreGrupo
FROM movimientos AS M
JOIN acreditados AS A
ON A.id_acreditado = M.id_acreditado
JOIN creditos AS C
ON C.id_credito = A.id_credito
JOIN abonos AS AB
ON AB.id_movimiento = M.id_movimiento
OUTER apply (SELECT TOP 1 G.nombre
FROM grupos G
WHERE G.id_credito = C.id_credito) tg
OUTER apply (SELECT TOP 1 P.nombres + ' ' + P.apellido_paterno + ' '
+ P.apellido_materno AS NombComp
FROM personas P
WHERE A.id_persona = P.id_persona) tp
GROUP BY M.fecha_mov,
AB.tipo_abono,
AB.id_deposito,
C.expediente,
C.status
ORDER BY M.fecha_mov
But it seems that MySQL has no OUTER APPLY or ISNULL. How can I translate this query to MySQL?

Answer 1

You have a couple of issues to review:
1 - The APPLY operator is not supported in MySQL. However, for your given usage, it looks like you can probably just use a LEFT OUTER JOIN.
2 - MySQL does not support TOP. Instead, use LIMIT. However, I don't think you need it in this case since you are using MIN of each of those fields.
3 - To concatenate strings in MySQL, use CONCAT vs "+".
4 - Finally, I prefer using COALESCE in MySQL to check for NULLs. There are other options though.
So putting it all together, this should be close (untested):
SELECT C.expediente,
C.status,
Sum(M.monto) AS monto,
Sum(M.interes) AS interes,
Sum(M.iva) AS iva,
Sum(M.capital) AS capital,
M.fecha_mov,
AB.tipo_abono,
AB.id_deposito,
COALESCE(MIN(tg.nombre), MIN(tp.nombcomp)) AS nombreGrupo
FROM movimientos AS M
JOIN acreditados AS A
ON A.id_acreditado = M.id_acreditado
JOIN creditos AS C
ON C.id_credito = A.id_credito
JOIN abonos AS AB
ON AB.id_movimiento = M.id_movimiento
LEFT OUTER JOIN (
SELECT id_credito, nombre
FROM grupos
) tg ON tg.id_credito = C.id_credito
LEFT OUTER JOIN (
SELECT id_persona, CONCAT(nombres,' ',apellido_paterno,' ',apellido_materno) AS NombComp
FROM personas
) tp ON A.id_persona = tp.id_persona
GROUP BY M.fecha_mov,
AB.tipo_abono,
AB.id_deposito,
C.expediente,
C.status
ORDER BY M.fecha_mov
You may not need some of those fields in your GROUP BY -- just your DISTINCT fields needed.

Answer 2

I think this turns it into a valid MySQL query:
SELECT C.expediente, C.status, Sum(M.monto) AS monto, Sum(M.interes) as interes,
Sum(M.iva) as iva, Sum(M.capital) as capital,
M.fecha_mov, AB.tipo_abono, AB.id_deposito,
coalesce(Min(tg.nombre), Min(tp.nombcomp)) AS nombreGrupo
FROM movimientos M join
acreditados A
ON A.id_acreditado = M.id_acreditado join
creditos C
ON C.id_credito = A.id_credito join
abonos AB
ON AB.id_movimiento = M.id_movimiento join
(select g.id_credito, max(g.nombre) -- arbitrary nombre
from grupos g
group by g.id_credito
) tg
on tG.id_credito = C.id_credito join
(SELECT P.id_persona, concat_ws(' ', P.nombres, P.apellido_paterno, P.apellido_materno) AS NombComp
FROM personas P
group by p.id_persona
) tp
on A.id_persona = tP.id_persona
GROUP BY M.fecha_mov, AB.tipo_abono, AB.id_deposito, C.expediente, C.status
ORDER BY M.fecha_mov
I replaced the isnull() with coalesce() -- if you are going between databases, use standard SQL where possible. I replaced the + for concatenation with concat_ws(). Note there is a small difference . . . if one of the fields is NULL, then the MySQL value will treat it as ''.
I replaced the cross apply with an aggregate. You use top 1 without an order by, so this fetches an arbitrary row. So, this version arbitrarily chooses the maximum value.