SQL - 如何简化这个简单的查询？

Question

我正在使用 SQL Server 2005。

我如何重构这个查询？

SELECT Total, Installs, Service, tot.ls_chg_dte_ojb
  FROM (SELECT COUNT(*) [Total], ls_chg_dte_ojb
         FROM [COMPL_INST_SVC]
         GROUP BY ls_chg_dte_ojb) tot

  JOIN (SELECT COUNT(*) [Service], ls_chg_dte_ojb
         FROM [COMPL_INST_SVC]
         WHERE job_class_ojb = 'S' 
         GROUP BY ls_chg_dte_ojb) svc on svc.ls_chg_dte_ojb = tot.ls_chg_dte_ojb

  JOIN (SELECT COUNT(*) [Installs], ls_chg_dte_ojb
         FROM [COMPL_INST_SVC]
         WHERE job_class_ojb in ('C', 'R') 
         GROUP BY ls_chg_dte_ojb) ins on ins.ls_chg_dte_ojb = tot.ls_chg_dte_ojb

Answer 1

看起来总数和服务计数正在计算相同的内容，因此您需要解决这个问题，但基本上以下是如何以更简单的方式进行计数：

SELECT
  COUNT(CASE WHEN job_class_ojb = 'S' THEN 1 END) AS [Total],
  COUNT(CASE WHEN job_class_ojb = 'S' THEN 1 END) AS [Service],
  COUNT(CASE WHEN job_class_ojb in ('C', 'R') THEN 1 END) AS [Installs]
FROM
  [COMPL_INST_SVC]

Answer 2

您的两个子选择是相同的。忽略“服务”一项，尝试以下方法

SELECT 
SUM(CASE WHEN job_class_ojb = 'S' THEN 1 ELSE 0 END) as Total,
SUM(CASE WHEN job_class_ojb = 'C' or
              job_class_ojb = 'R' THEN 1 ELSE 0 END) as Installs
FROM COMPL_INST_SVC

Answer 3

我怀疑 Totals 子查询不应包含 WHERE job_class_ojb = 'S' 条件 - 如果是这样，我建议：

SELECT COUNT(*) Total,
       SUM(CASE WHEN job_class_ojb = 'S' THEN 1 ELSE 0 END) Service,
       SUM(CASE WHEN job_class_ojb in ('C','R') THEN 1 ELSE 0 END) Installs,
       ls_chg_dte_ojb
FROM COMPL_INST_SVC
GROUP BY ls_chg_dte_ojb