在 mysql 查询中获得一个额外的变量

Question

I am using Laravel and I am working on an existing project where I got a query

SELECT SUM(multi) as total
FROM ( SELECT men*hours as multi FROM report_task_manhours WHERE task_id=27013)X

Can anyone explain what is the use of X which is present in last in the query?

And it's working when I run this query in MySQL console.

Answer 1

X is working as an alias of your subquery which is below

( select men*hours as multi from report_task_manhours where task_id=27013)

So if you want to use any of the other fields from your subquery to your main query then you need to use it with X.{field_name} as you can also use X.multi inside SUM function in your main query.

Like below

select sum(X.multi) as total from ( select men*hours as multi from report_task_manhours where task_id=27013)X

I hope it's clear.