优化查询仍需要多长时间

Question

如何优化此查询？我曾尝试使用LEFT JOIN条款，但仍至少需要3秒。

SELECT DISTINCT MBLNR 
FROM MKPF 
WHERE MANDT='368' 
    AND XBLNR = '0150525913' 
    AND MBLNR NOT IN (SELECT DISTINCT SMBLN FROM MSEG WHERE XBLNR_MKPF = '0150525913') 

使用LEFT JOIN后，仍需要3秒，得到的结果：

SELECT DISTINCT A.MBLNR 
FROM MKPF AS A 
LEFT JOIN MSEG AS B ON B.XBLNR_MKPF=A.XBLNR AND A.MBLNR <> B.SMBLN 
WHERE A.XBLNR = '0150525913' 

使用LEFT OUTER JOIN真的要花很多时间来返回行。

谢谢。

Answer 1

正确的左外连接第一个查询的提法是：

SELECT DISTINCT A.MBLNR 
FROM MKPF A LEFT JOIN 
    MSEG B 
    ON B.SMBLN = A.MBLNR AND AND B.XBLNR_MKPF = '0150525913' 
WHERE A.XBLNR = '0150525913' and A.MANDT='368' and B.SMBLN is null; 

根据表的大小，3秒后可能是合理的。但是，您可以使用索引加速查询。该查询建议一些索引：MKPF(XBLNR, MANDT, MBLNR)和MSEG(XBLNR_MKPF, SMBLN)。

Answer 2

虽然直观，“不在”是缓慢的。你为什么要使用不同的和left.If他们真的需要那么其确定。或者你可以使用内部连接无明显.Specially子查询不

AND MBLNR NOT IN 
(SELECT DISTINCT SMBLN FROM MSEG WHERE XBLNR_MKPF = '0150525913') 

到

AND MBLNR IN 
(SELECT DISTINCT MBLNR 
FROM MKPF 
WHERE MANDT='368' 
AND XBLNR = '0150525913' 
except 
SELECT DISTINCT SMBLN 
FROM MSEG 
WHERE XBLNR_MKPF = '0150525913' 
) 

Answer 3

：所以，改变这种需要明确。

you can try not exists 
SELECT MBLNR 
FROM MKPF 
WHERE MANDT='368' 
    AND XBLNR = '0150525913' 
    AND NOT exists (SELECT SMBLN FROM MSEG WHERE XBLNR_MKPF = '0150525913')