mysql - 局部变量和前面的列

Question

我试图在查询中使用 @variable1 + @variable2 但实际上给出的结果是 0。

玛丽亚数据库 服务器版本:10.2.21

set @start_at = '2019-01-01';
set @end_at = '2019-01-16';
set @receivable = 0;
set @invoiced = 0;
SELECT DISTINCT Customer.custnr 'Customer Number',
                Address.name    'Name',
                @receivable := sum(case
                      WHEN [condition1 <= @start_at]
                        AND Transactions.`key` not in [subquery]
                        THEN Transactions.amount
                      ELSE 0 END) 'Account Receivable',
                @invoiced := sum(case
                      WHEN [condition1 between @start_at and @end_at]
                        AND [condition2]
                        AND [condition3]
                        AND Transactions.`key` not in [subquery]
                        THEN Transactions.amount
                      ELSE 0 END) 'Invoiced',
                @receivable + @invoiced 'Total'
FROM LocalCust
       INNER JOIN Customer
                  on Customer.`key` = LocalCust.customerkey
       INNER JOIN Address
                  on Address.`key` = Customer.addresskey
       INNER JOIN Location
                  on Location.`key` = LocalCust.localkey
       INNER JOIN Transactions
                  on Transactions.localcustkey = LocalCust.`Key`
GROUP BY Transactions.localcustkey;

结果:

Answer 1

使用子查询，完全不使用变量:

SELECT x.*, (Account_Receivable + Invoice) as Total
FROM (SELECT c.custnr as Customer_Number, a.name, 
             sum(case when condition1 <= @start_at and
                           t.`key` not in [subquery]
                      then t.amount
                      else 0 
                 end) as Account_Receivable,
             sum(case when condition1 between @start_at and @end_at and
                           [condition2] and
                           [condition3] and
                           t.`key` not in [subquery]
                      then t.amount
                      else 0 
                 end) as Invoiced
      FROM LocalCust lc JOIN
           Customer c
           on c.`key` = lc.customerkey JOIN
           Address a
           on a.`key` = c.addresskey JOIN
           Location l
           on l.`key` = lc.localkey join
           Transactions t
           on t.localcustkey = lc.`Key`
      GROUP BY c.custnr, a.name
     ) x;

注意事项:

• 表别名使查询更易于编写和阅读。
• SELECT DISTINCT 几乎不需要 GROUP BY。
• GROUP BY 键应与 SELECT 中的未聚合列相匹配。
• 选择不需要转义的列别名。也就是说，没有空格。