BIRT SQL Null 案例场景答案

【问题标题】：BIRT SQL Null Case ScenarioBIRT SQL Null 案例场景
【发布时间】：2015-02-23 11:27:11
【问题描述】：

我正在使用以下 SQL 语句来检索有关工单的各种信息。但是，其中一些没有列出资产（NULL），在这种情况下，我得到 0 行：

select PM17, WORKORDER.PMNUM, WORKORDER.ASSETNUM, ASSET.DESCRIPTION, ASSET.MANUFACTURER, EQASSETNUM, WORKORDER.LOCATION, LOCATIONS.DESCRIPTION, PM.ROUTE, TARGSTARTDATE, TARGCOMPDATE, PM.NEXTDATE
from WORKORDER 
JOIN ASSET ON WORKORDER.ASSETNUM = ASSET.ASSETNUM
JOIN PM ON WORKORDER.PMNUM = PM.PMNUM
JOIN LOCATIONS ON WORKORDER.LOCATION = LOCATIONS.LOCATION
WHERE WORKORDER.WONUM='1011';

如何修改我的语句以适用于这两种情况（有或没有 ASSETNUM）？

案例 1 (ASSETNUM != NULL)--> 显示所有选择的字段

案例 2 (ASSETNUM = NULL) --> 显示不依赖于 ASSETNUM 的字段，其余部分返回 null

【问题讨论】：

标签： sql birt

【解决方案1】：

将您的 JOIN 更改为 LEFT JOIN：

select PM17, WORKORDER.PMNUM, WORKORDER.ASSETNUM, ASSET.DESCRIPTION, ASSET.MANUFACTURER, EQASSETNUM, WORKORDER.LOCATION, LOCATIONS.DESCRIPTION, PM.ROUTE, TARGSTARTDATE, TARGCOMPDATE, PM.NEXTDATE
from WORKORDER 
LEFT JOIN ASSET ON WORKORDER.ASSETNUM = ASSET.ASSETNUM
JOIN PM ON WORKORDER.PMNUM = PM.PMNUM
JOIN LOCATIONS ON WORKORDER.LOCATION = LOCATIONS.LOCATION
WHERE WORKORDER.WONUM='1011';

【讨论】：