Question

我有一个包含character varying个字段的表格-

Bill    Render     Refer        Supervise
        1194772160  
        1538359872  
        1194772160  
        1104026103  
        1104026103  
                                1831124015
        1740237197  1740237197  1740237197

下面的查询为什么返回空字符串-

SELECT
    CASE
        WHEN render != bill THEN render
    END AS renderUnique

Answer 1

如果要将空值比较为相等，请使用function imageSizeAfterRotation(size, degrees) { degrees = degrees % 180; if (degrees < 0) { degrees = 180 + degrees; } if (degrees >= 90) { size = [ size[1], size[0] ]; degrees = degrees - 90; } if (degrees === 0) { return size; } const radians = degrees * Math.PI / 180; const width = (size[0] * Math.cos(radians)) + (size[1] * Math.sin(radians)); const height = (size[0] * Math.sin(radians)) + (size[1] * Math.cos(radians)); return [ width, height ]; } // USAGE: imageSizeAfterRotation([ 200, 80 ], 30) // [ 213.20508075688775, 169.28203230275508 ]：

IS [NOT] DISTINCT FROM

请注意，SELECT CASE WHEN render IS DISTINCT FROM bill THEN render END AS renderUnique大致意味着x与y不同。真相表应该有帮助：

x IS DISTINCT FROM y

Answer 2

由于null列的所有行都包含bill，因此比较：

render != bill

等效于：

render != null

返回null，因此不是true，并且case语句返回null。
您可以将其更改为：

select 
(CASE WHEN coalesce(render, '') != coalesce(bill, '') THEN render END) as renderUnique

在CASE中比较字符串

2 个答案: