Question

当我运行以下查询时，我收到错误“无法将VARCHAR转换为FLOAT”。问题是我的团队中的其他人设计了DB一段时间，并将毫秒作为varchar和sSometime，因为他没有设置值，所以他改为“NA”。

现在，当我将毫秒的值转换为AVE（）时，“NA”无法生成。有没有办法为“NA”定义默认值，如：

IF a.Milliseconds == "NA" 
     0
ELSE
     CAST(a.Milliseconds AS FLOAT)



SELECT 
  b.Date, 
  AVG(CAST(a.Milliseconds AS FLOAT)) AS Milliseconds,
FROM Fields a
INNER JOIN Cycles b
ON a.CyclesId = b.Id
GROUP BY b.Date

Sample Data

CyclesId | Milliseconds
1        | 24.1557
2        | 23.4886
3        | NA

Answer 1

在您的值周围使用CASE语句

SELECT 
  b.Date, 
  AVG(CAST(CASE WHEN a.Milliseconds = 'NA' THEN '0' ELSE a.Milliseconds END AS FLOAT)) AS Milliseconds,
FROM Fields a
INNER JOIN Cycles b
    ON a.CyclesId = b.Id
GROUP BY b.Date

如果您希望将NA值排除在一起，那么您将执行以下操作：

SELECT 
  b.Date, 
  AVG(CAST(a.Milliseconds AS FLOAT)) AS Milliseconds,
FROM Fields a
INNER JOIN Cycles b
    ON a.CyclesId = b.Id
WHERE a.Milliseconds != 'NA'
GROUP BY b.Date

通过演示

查看SQL Fiddle

Answer 2

使用CASE ...例如......

SELECT 
  b.Date, 
  AVG(CAST( (case when a.Milliseconds = 'NA' then 0 else a.Milliseconds end) AS FLOAT)) AS Milliseconds,
FROM Fields a
INNER JOIN Cycles b
ON a.CyclesId = b.Id
GROUP BY b.Date

用于FLOAT的SQL条件转换VARCHAR

2 个答案: