Question

我需要有关原始SQL查询的帮助，该查询根据另一个值获取值。

我有以下原始SQL查询。

SELECT pmPropDef.id, pmPropDef.name, pmPropDef.units, pmPropShort.str, pmPropLong.str   
 FROM pmProp INNER JOIN pmPropDef ON pmProp.propid=pmPropDef.id AND pmPropDef.name = 'Area' 
 LEFT JOIN pmPropShort ON sid=pmProp.value 
 LEFT JOIN pmPropLong ON lid=-pmProp.value 
 WHERE pmProp.ownertype='variant' AND pmPropDef.id = pmProp.propid;

这导致以下结果：

+----+------+-------+------+------+
| id | name | units | str  | str  |
+----+------+-------+------+------+
| 14 | Area | mm2   | 1.1  | NULL |
+----+------+-------+------+------+

我得到了pmPropShort.str和pmPropLong.str的问题，我应该打赌一个或另一个。我真正想要的是一个单一的价值？如何重新编写此查询以满足我的需求？

Answer 1

您可以使用COALESCE返回第一个非NULL参数。例如。

COALESCE(pmPropShort.str, pmPropLong.str)

Answer 2

你有明显的优先权吗？

示例如果long是优先级

SELECT pmPropDef.id, pmPropDef.name, pmPropDef.units, 
 IF(pmPropLong.str IS NOT NULL,pmPropLong.str,pmPropShort.str) as str
FROM ...rest of your query

MySQL - 合并两个连接结果

2 个答案: