where子句中的mysql变量

Question

当我添加最后一行“和@summ＆gt; 0 （任何条件）”时 它返回空结果。 我做错了什么？如何将 @summ 传递给where子句？

 select
      nore.nis as nore_curent,
      field_funds.value,
     (select @summ :=
        sum(field_amount.value - field_amount_tip.value)
          from
        nore
        inner join field_project on nore.nis = field_project.id
        inner join field_funds on field_funds.id = field_project.target_id
        inner join field_amount on nore.nid = field_data_field_amount.id
        inner join field_amount_tip on nore.nis = field_amount_tip.id
          where
        nore.`s` = 1
          and
        nore.`t` = 'p'
          and
        field_project.target_id = nore_curent) as amount
      from
       nore
      inner join field_funds on nore.nis = field_funds.id
       where
      nore.`s` = 1
       and
      nore.`t` = 'pp'
       and @summ > 0

Answer 1

值得重新记录一些与Select语句的概念（或逻辑）评估顺序相关的基础知识 - 这里：http://tinman.cs.gsu.edu/~raj/sql/node22.html

订单是：

1. FROM
2. WHERE
3. GROUP BY
4. HAVING
5. ORDER BY
6. SELECT


在 SELECT子句之前评估（执行） WHERE子句 值@summ在SELECT子句（主查询）中计算，因此当DMBS评估WHERE子句时，它的值是未知的。

未知= NULL

因此，此查询将无法按预期工作。

将查询重写为：

select
      nore.nis as nore_curent,
      field_funds.value,
     (select sum(field_amount.value - field_amount_tip.value)
          from
        nore
        inner join field_project on nore.nis = field_project.id
        inner join field_funds on field_funds.id = field_project.target_id
        inner join field_amount on nore.nid = field_data_field_amount.id
        inner join field_amount_tip on nore.nis = field_amount_tip.id
          where
        nore.`s` = 1
          and
        nore.`t` = 'p'
          and
        field_project.target_id = nore_curent) as amount
      from
       nore
      inner join field_funds on nore.nis = field_funds.id
       where
      nore.`s` = 1
       and
      nore.`t` = 'pp'
       and 0 < (select sum(field_amount.value - field_amount_tip.value)
                  from nore
                  inner join field_project on nore.nis = field_project.id
                  inner join field_funds on field_funds.id = field_project.target_id
                  inner join field_amount on nore.nid = field_data_field_amount.id
                  inner join field_amount_tip on nore.nis = field_amount_tip.id
                  where
                    nore.`s` = 1
                    and
                    nore.`t` = 'p'
                    and
                    field_project.target_id = nore_curent
)