如何按年计算两个字段

Question

我想按年计算两个字段

我试试

SELECT YEAR(admit_date),COUNT(sub_case),COUNT(SK) 
FROM admit 
WHERE sub_case = "scase001" 
  AND SK = "rsk002"
GROUP BY YEAR(admit_date),sub_case,SK

但事实并非如此

表

总计

真

2014 1 0
2015 1 1

Answer 1

您需要从GROUP BY

中删除sub_case和SK列

SELECT YEAR(admit_date),COUNT(sub_case),SUM(CASE WHEN SK="rsk002" THEN 1 ELSE 0 END)
FROM admit 
WHERE sub_case = "scase001" 
GROUP BY YEAR(admit_date)

Answer 2

您可以使用条件聚合，如下所示：

SELECT 
  YEAR(admit_date) AS "admit_year",
  SUM(sub_case = 'scase001') AS "sub_case_count",
  SUM(SK = 'rsk002') AS "sk_count"
FROM admit
GROUP BY YEAR(admit_date)

对于所有匹配的行，表达式sub_case = 'scase001'将评估为1，并且总结匹配与计算它们相同。以这种方式使用（或滥用）布尔表达式可能在其他SQL数据库中不起作用，但它在MySQL中起作用（通常会使用case when ... then .. end表达式。）