Question

我对我的SELECT感到困惑：

SELECT  
    mergedData.rawValue,
    mergedData.validatedValue,
    IFNULL(mergedData.validatedValue, mergedData.rawValue) as mergedValue
FROM
    [...]

当mergedData.rawValue和mergedData.validatedValue返回DOUBLE时，IFNULL语句返回BLOB。为什么会这样？我怎样才能让它返回DOUBLE呢？

编辑：我通过模拟FULL JOIN合并了两个在我的Select中具有完全相同结构的表。数据在两个表中都存储为DOUBLE：

TableRawData（NOX加载到mergedData.rawValue中）：

timed (BIGINT(20)) --- NOX (DOUBLE)
1380583800000          8.972167

TableValidatedData（NOX加载到mergedData.validatedValue中）：

timed (BIGINT(20)) --- NOX (DOUBLE)
1380583800000          9.506166

EDIT2：我的完整选择：

SET @StartTime  = 1356998400000;
SET @EndTime    = 1386546000000;

SELECT  
    mergedData.rawValue,
    mergedData.validatedValue,
    CAST(IFNULL(mergedData.validatedValue, mergedData.rawValue) AS DECIMAL(10, 5)) as mergedValue
FROM
 (SELECT 
        Month(FROM_UNIXTIME(timed / 1000)) as months,
            Year(FROM_UNIXTIME(timed / 1000)) as years,
            DAYOFMONTH(FROM_UNIXTIME(timed / 1000)) as days,
            HOUR(FROM_UNIXTIME(timed / 1000)) as hours,
            MINUTE(FROM_UNIXTIME(timed / 1000)) as minutes,
            IF(true, avg(NOX), null) as rawValue,
            FROM_UNIXTIME(timed / 1000) as timeValue,
            IF(true, 1, 0) as IsValid,
            NULL as validatedValue
    FROM
        nabelnrt_bas
    WHERE
        timed > @StartTime
            AND timed < @EndTime
    GROUP BY concat(years, months, days) UNION (
 SELECT 
        Month(FROM_UNIXTIME(timed / 1000)) as months,
            Year(FROM_UNIXTIME(timed / 1000)) as years,
            DAYOFMONTH(FROM_UNIXTIME(timed / 1000)) as days,
            HOUR(FROM_UNIXTIME(timed / 1000)) as hours,
            MINUTE(FROM_UNIXTIME(timed / 1000)) as minutes,
            IF(true, avg(NOX), null) as validatedValue,
            FROM_UNIXTIME(timed / 1000) as timeValue,
            IF(true, 1, 0) as IsValid,
            NULL as rawValue
    FROM
        nabelvalidated_bas
    WHERE
        timed > @StartTime
            AND timed < @EndTime
    GROUP BY concat(years, months, days))) as mergedData

Answer 1

投下它

SELECT  
    mergedData.rawValue,
    mergedData.validatedValue,
    CAST(IFNULL(mergedData.validatedValue, mergedData.rawValue) AS DECIMAL[(M[,D])]) as mergedValue
FROM

请注意DECIMAL[(M[,D])]您应该在定义表时填写它。

编辑，COALESCE也可能很有趣。示例用法;

SELECT  
    mergedData.rawValue,
    mergedData.validatedValue,
    COALESCE(mergedData.validatedValue, mergedData.rawValue) as mergedValue
FROM

Perheps你不需要再施展

DOUBLE以BLOB的形式返回

1 个答案: