Question

这应该相当简单，但在搜索时找到合适的术语是很棘手的。

在下面的查询中，如果WHERE lang='en'没有返回任何内容，我只需要选择WHERE lang='nl_NL'。换句话说，我想查找所有记录WHERE script='generic'，按lang=nl_NL

划分优先顺序

SELECT * FROM international WHERE script='generic' AND (lang = 'nl_NL' OR lang = 'en')

Answer 1

SELECT * FROM international WHERE script = 'generic' AND lang = CASE
  WHEN EXISTS(
    SELECT 1
    FROM   international
    WHERE  script = 'generic'
       AND lang   = 'nl_NL'
    LIMIT  1
  ) THEN 'nl_NL'
  ELSE 'en'
END

Answer 2

以下是获取指定结果集的一种方法示例：

SELECT i.*
  FROM international i
 WHERE i.lang = 'nl_NL'
    OR (i.lang = 'en' 
        AND NOT EXISTS 
        (SELECT 1 FROM international d WHERE d.lang = 'nl_NL')
       )

当你想要应用“script='generic'”谓词时，你的问题并不清楚。

SELECT i.*
  FROM international i
 WHERE ( i.script = 'generic' AND i.lang = 'nl_NL')
    OR ( i.script = 'generic' AND i.lang = 'en'
         AND NOT EXISTS 
           ( SELECT 1
               FROM international d
              WHERE d.lang = 'nl_NL'
                AND d.script='generic'
           )
       )

mySQL选择优先级 - 选择一行或另一行（选择默认或“后备”行）

2 个答案: