SQL-如何简化此简单查询？

Question

I am using SQL Server 2005.

How could I refactor this query?

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

Two of your sub-selects are the same. Ignoring the 'Service' one, try something along the lines of

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 2

It looks like the Total and Service counts are counting the same exact thing, so you'll need to fix that, but here's basically how you do the counts in a simpler way:

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 3

I suspect that the Totals subquery should not include the WHERE job_class_ojb = 'S' condition - if so, I suggest:

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