Question

这就是我想要做的：

SELECT
  id, text, the_match
FROM
  comments
WHERE
  (lower(text) LIKE '%excellent%'
   OR lower(text) LIKE '%great%'
   OR lower(text) LIKE '%good%') AS the_match
ORDER BY len(text) ASC

SQL无效。 the_match不是有效的列。我正在尝试显示WHERE子句中的哪个条件导致匹配。我该怎么办？

Answer 1

您可以使用CASE表达式：

SELECT
    id,
    text,
    CASE WHEN LOWER(text) LIKE '%excellent%' THEN 'excellent'
         WHEN LOWER(text) LIKE '%great%'     THEN 'great'
         WHEN LOWER(text) LIKE '%good%'      THEN 'good' END the_match
FROM comments
WHERE
    LOWER(text) LIKE '%excellent%' OR
    LOWER(text) LIKE '%great%' OR
    LOWER(text) LIKE '%good%'
ORDER BY
    LEN(text);

如果您想为comments表中的每个记录添加标签，则只需删除WHERE子句。在这种情况下，对于不匹配的记录，the_match字段将为NULL。

Answer 2

您不能直接这样做（如您所见）。解决此类问题的一种方法是在选择列表中使用具有相同条件的case表达式：

SELECT
  id, text, CASE WHEN lower(text) LIKE '%excellent%' THEN 'excellent condition'
                 WHEN lower(text) LIKE '%great%'     THEN 'great condition'
                 WHEN lower(text) LIKE '%good%'      THEN 'good condition'
            END AS condition
FROM
  comments
WHERE
  (lower(text) LIKE '%excellent%'
   OR lower(text) LIKE '%great%'
   OR lower(text) LIKE '%good%') AS the_match
ORDER BY len(text) ASC

为避免逻辑重复，可以将其移至子查询：

SELECT    id, text, condition
FROM      (SELECT id, 
                  text, 
                  CASE WHEN LOWER(text) LIKE '%excellent%' THEN 'excellent'
                       WHEN LOWER(text) LIKE '%great%'     THEN 'great'
                       WHEN LOWER(text) LIKE '%good%'      THEN 'good'
                  END AS condition
           FROM   comments ) t
WHERE    condition IS NOT NULL
ORDER BY LEN(text) ASC

Answer 3

将where转换为case：

SELECT
  id, text, 
  case
    when lower(text) LIKE '%excellent%' then 'excellent'
    when lower(text) LIKE '%great%' then 'great'
    else 'good' end as the_match
FROM
  comments
WHERE
  lower(text) LIKE '%excellent%'
   OR lower(text) LIKE '%great%'
   OR lower(text) LIKE '%good%'
ORDER BY len(text) ASC

请注意，the_match返回找到的“最高”优先级单词。也就是说，如果text既有“好”又有“好”，那么the_match就是“好”。

如何显示哪个WHERE条件匹配？

3 个答案: