强制查询结果为真

Question

我有一个如下查询：

SELECT cust.adm, COUNT(visits.visit_date) as visit_count FROM cust
LEFT JOIN visits ON cust.cust_id = visits.cust_id
WHERE cust.cust_id = 1
GROUP BY cust.adm

结果是：

   adm   |   visit_count
--------------------------
  TRUE   |        0

如果adm为true，是否可以在'visit_count'上强制结果为'3'？

Answer 1

您可以使用case表达式：

SELECT    cust.adm,
          CASE cust.adm WHEN TRUE THEN 3 ELSE COUNT(visits.visit_date) END AS visit_count 
FROM      cust
LEFT JOIN visits ON cust.cust_id = visits.cust_id
WHERE     cust.cust_id = 1
GROUP BY  cust.adm

Answer 2

这确实是迫使它。我能想到的就是不知道您要实现的目标。

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