Question

我有两张桌子，我想加入，但我不知道如何让它最有效率。

任务表：

userid | name
  11   |  EmployeeA
  22   |  EmployeeB
  33   |  EmployeeC

员工表：

userid | created_count | claimed_count | urgent_count
  11   |       3       |       1       |       3
  22   |       1       |       1       |       2
  33   |       1       |       1       |       2

结果我想得到：

created_account

claimed_count列将显示该用户创建的任务总数。

urgent_count列将显示该用户声明的总任务数。

test/15-test列将显示该用户的紧急任务总数（已创建或已声明）。

提前致谢！

Answer 1

我首先将它分解成碎片，然后将它们重新组合在一起。您可以使用这样的简单聚合获取created_count和claims_count：

SELECT created_by, COUNT(*) AS created_count
FROM myTable
GROUP BY created_by;

SELECT claimed_by, COUNT(*) AS claimed_count
FROM myTable
GROUP BY claimed_by;

为了获得每个员工的紧急计数，我会加入这两个表，条件是员工是created_by或claim_by列，并且是员工。但是，我会使用SUM()而不是计算。我这样做是因为它看起来每行都是0或1，所以SUM（）将有效地计算所有非零行：

SELECT e.userid, SUM(t.urgent)
FROM employee e
JOIN task t ON e.userid IN (t.created_by, t.claimed_by)
GROUP BY e.userid;

现在您拥有了所需的所有数据，您可以使用外部联接将所有这些子查询连接到employees表以获取其计数。您可以使用COALESCE()函数将任何空计数替换为0：

SELECT e.userid, COALESCE(u.urgent_count, 0) AS urgent_count, COALESCE(crt.created_count, 0) AS created_count, COALESCE(clm.claimed_count, 0) AS claimed_count
FROM employee e
LEFT JOIN(
  SELECT e.userid, SUM(t.urgent) AS urgent_count
  FROM employee e
  JOIN task t ON e.userid IN (t.created_by, t.claimed_by)
  GROUP BY e.userid) u ON u.userid = e.userid
LEFT JOIN(
  SELECT claimed_by, COUNT(*) AS claimed_count
  FROM task
  GROUP BY claimed_by) clm ON clm.claimed_by = e.userid
LEFT JOIN(
  SELECT created_by, COUNT(*) AS created_count
  FROM task
  GROUP BY created_by) crt ON crt.created_by = e.userid;

以下是SQL Fiddle示例。

获取具有mysql连接和2个表的记录总数

1 个答案: