BIRT SQL Null案例场景

Question

我使用以下SQL语句检索工单上的各种信息。但是，他们中的一些人没有列出资产（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';

如何修改我的陈述以适用于两种情况（有或没有ASSETNUM）？

案例1（ASSETNUM！= NULL） - ＆gt;显示所有选定的字段

案例2（ASSETNUM = NULL） - ＆gt;显示不依赖于ASSETNUM的字段，并为其余字段返回null

Answer 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';