Question

基本上我想遍历数据库中的所有0，然后再开始遍历2。

查询为：

   SELECT IP,Time,HostName
     FROM RoughScan
CASE WHEN EXISTS (DeepScan=0) 
     THEN (DeepScan=0 LIMIT 1) 
     ELSE (DeepScan=2 LIMIT 1)

但我收到错误消息：

CASE表达式的意外结尾（位置“ 0”附近的“”附近）

我也在使用MariaDB服务器。

Answer 1

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union all

请注意，(SELECT `IP`,`Time`,`HostName` FROM `RoughScan` WHERE DeepScan = 0 LIMIT 1 ) UNION ALL (SELECT `IP`,`Time`,`HostName` FROM `RoughScan` WHERE DeepScan = 2 LIMIT 1 );通常与ORDER BY一起使用。

Answer 2

您需要像这样将CASE应用于WHERE：

SELECT IP,Time,HostName
FROM RoughScan
WHERE 
  DeepScan = CASE 
    WHEN EXISTS (SELECT 1 FROM RoughScan WHERE DeepScan = 0) THEN 0 
    ELSE 2 
  END
LIMIT 1

SQL-查询期间的条件

2 个答案: