I am using MySQL 5-enterprise-commercial
version.
I have written the below 2 queries which I want to convert into a single query using join.
SET @row_number :=0;
SELECT
@row_number:= case
when @RId = r_id then @row_number 1
else 1
end as rnum,
@RId:=r_id as r_id,
msg,
supplier,
rrtry from (
SELECT
a.r_id as r_id,
mta.message as msg,
tpr.supplier as supplier,
trw.retry as rrtry,
a.createdAt as createdAt,
FROM sa.nra a,
sa.nmta mta,
sa.treq tpr,
sa.twflw trw
WHERE tpr.n_r_id = a.r_id
AND trw.astp = mta.stp
AND mta.rstatus in ('FAIL')
AND tpr.p_w_id = trw.id
AND a.a_mid = mta.id
AND a.createdAt BETWEEN now() - interval 30 DAY AND now()
ORDER BY a.r_id
) as sa
HAVING rnum = 1
ORDER BY createdAt DESC;
Basically, there are multiple entries for r_id
, and I want to get the latest entry for a particular r_id
and that is why I am using ORDER BY a_createdAt DESC
CodePudding user response:
Join the query with a subquery that uses the :=
operator to set the variable.
SELECT
@row_number:= case
when @RId = r_id then @row_number 1
else 1
end as rnum,
@RId:=r_id as r_id,
msg,
supplier,
rrtry
from (
SELECT
a.r_id as r_id,
mta.message as msg,
tpr.supplier as supplier,
trw.retry as rrtry,
a.createdAt as createdAt
FROM sa.nra a
JOIN sa.nmta mta ON a.a_mid = mta.id
JOIN sa.treq tpr ON tpr.n_r_id = a.r_id
JOIN sa.twflw trw ON trw.astp = mta.stp AND tpr.p_w_id = trw.id
WHERE mta.rstatus in ('FAIL')
ORDER BY a.r_id
) as sa
CROSS JOIN (SELECT @row_number := 0) AS vars
HAVING rnum = 1
ORDER BY a_createdAt DESC;
I've replaced the cross-product in the subquery with ANSI JOIN.
If you're using MySQL 8.0, you can use the RANK()
or ROW_NUMBER()
window functions instead of a user variable.