查询加入问题

Question

为什么此查询从两个表而不是仅从OVPM返回？

SELECT * 
from OVPM M1 
JOIN VPM2 M2 ON M2.DocNum = M1.DocNum 
AND Canceled = 'N' 
WHERE M1.DocNum = '2292' 

Answer 1

因为您查询了所有内容*。如果你只需要OVPM的数据 - 用M1.*