mysql - where子句中的Mysql变量

Question

当我添加最后一行“和@summ > 0（任何条件）”时，它返回空结果。我做错了什么？如何正确地将@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

保留一些与 Select 语句评估的概念（或逻辑）顺序相关的基础知识是值得的 - 在这里：http

://tinman.cs.gsu.edu/~raj/sql/node22.html顺序是：

1. 从
2. 在哪里
3. 通过...分组
4. 拥有
5. 订购方式
6. 选择

WHERE 子句在 SELECT 子句之前 评估（执行） 。
的值@summ是在（主查询的）SELECT 子句中计算的，因此当 DMBS 评估 WHERE 子句时，它的值是未知的。

Unknown = NULL

因此此查询不会按预期工作。

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
)