在这个Query的帮助下我想要一些null结果

Question

查询

SELECT
  CASE
  WHEN `tomato_rating` = 0 THEN 'NULL'
  WHEN `tomato_rating` != 0 THEN `tomato_rating`
  END `tomato_rating`,
  ur.`user_rating`, 
  ABS(tomato_rating - ur.`user_rating`) AS avg_guess_error  
FROM user_rating ur
  LEFT JOIN videos v
    ON ur.vid_id = v.id
WHERE ur.user_id = '1'

查看结果屏幕截图进行验证

结果必需

NULL - 50 NULL
50   - 30 20
65   - 33 32
NULL - 16 NULL

Answer 1

如果我理解了您的问题，您希望NULL tomato_rating = 0返回{。}}。

为此，您可以使用NULLIF功能：

SELECT
  NULLIF(`tomato_rating`, 0) AS `tomato_rating`,
  ur.`user_rating`, 
  ABS(NULLIF(`tomato_rating`, 0) - ur.`user_rating`) AS avg_guess_error  
FROM user_rating ur
  LEFT JOIN videos v
    ON ur.vid_id = v.id
WHERE ur.user_id = '1'

Answer 2

我认为这就是你要找的东西：

SELECT
  IF (`tomato_rating` = 0, 'NULL', `tomato_rating`) as `tomato_rating`,
  ur.`user_rating`,
  IF (`tomato_rating` = 0, 'NULL', ABS(tomato_rating - ur.`user_rating`))
    as avg_guess_error  
FROM user_rating ur
LEFT JOIN videos v ON ur.vid_id = v.id
WHERE ur.user_id = '1'

请注意，您使用的是字符串'NULL'，而不是NULL。

Answer 3

这是你要找的吗？

SELECT
CASE
WHEN `tomato_rating` = 0 THEN 'NULL'
WHEN `tomato_rating` != 0 THEN `tomato_rating`
END `tomato_rating`,
ur.`user_rating`, 
CASE
WHEN `tomato_rating` = 0 THEN 'NULL'
WHEN `tomato_rating` != 0 THEN ABS(tomato_rating - ur.`user_rating`) 
END `avg_guess_error`,  
FROM user_rating ur
LEFT JOIN videos v
ON ur.vid_id = v.id
WHERE ur.user_id = '1'