Question

我有3个表项目，时间和费用。我想加入其中的所有3个并计算总和以及检索所有匹配的记录。

以下是我的表格：

projects:
id      name
=====================
1       First Project
2       Second Project

times:
id      project_id  hours       billed
===================================================
1       1           2.0         1
2       1           3.0         0
3       2           4.30        0

expense:
id      project_id  amount         billed
==================================================
1       1           120.00         0
2       2           35.00          1
3       2           55.00          0
4       2           45.00          0

这是我的疑问：

  SELECT 
    SUM(t.hours) as total_hours,
    SUM(e.amount) as total_amount,
    p.name
  FROM
    `projects` AS p 
    LEFT JOIN `expense` AS e 
      ON e.project_id = p.id
    LEFT JOIN `times` AS t 
      ON t.project_id = p.id 
  WHERE t.billed = 0
  AND e.billed = 0
  GROUP BY p.id;

但由于某种原因，我无法让它发挥作用，我最终没有记录。

结果应该类似于：

Name            Total Hours     Total Expense
==============================================
First Project   3.00             120.00
----------------------------------------------
Second Project  7.30             100.00
----------------------------------------------

Answer 1

你只是错误地使用表别名：

SELECT 
    SUM(e.hours) as total_hours,
    SUM(t.amount) as total_amount,
    p.name
  FROM
    `projects` AS p 
    LEFT JOIN `expense` e 
      ON e.project_id = p.id
    LEFT JOIN `times` t 
      ON t.project_id = p.id 
  WHERE t.billed = 0
  AND e.billed = 0
  GROUP BY p.id;

按预期工作：http://sqlfiddle.com/#!9/48bfd1/3

Php，MySql连接3个表，并计算SUM

1 个答案: