Question

使用此架构：

CREATE TABLE LookUp
([docID] varchar(10), [docType] varchar(100), [PartNumber] varchar(100), [internalID] varchar(100));
INSERT INTO LookUp
([docID],[docType],[PartNumber], [internalID])
VALUES
('D0305415', 'docTypeSub', 'X0455', null),
('D0157632', 'docTypeMain', null, 'XY05570-XY05571'),
('D0181511', 'docTypeMain',null, 'XY05572-XY05573'),
('D0157633', 'docTypeMain',null, 'XY06380-XY06381'),
('D0156037', 'docTypeSub', 'X0326', null),
('D0151874', 'docTypeMain', null, 'XY05345');

CREATE TABLE Links
([docIDTop] varchar(10), [docIDBottom] varchar(10));
INSERT INTO Links
([docIDTop],[docIDBottom])
VALUES
('D0157632', 'D0305415'),
('D0181511', 'D0305415'),
('D0157633', 'D0305415'),
('D0151874', 'D0156037');

有没有办法优化这个查询而不使用嵌套的'select'，我认为有一种方法，但我记不清了; P。 Lookup表中有一对多关系，当doctype为'doctypeSub'时，有一个主行，在链表中用于与查询表（再次）及其详细信息的关系。

SELECT * FROM
(SELECT INTERNALID,
(SELECT PARTNUMBER 
 FROM LOOKUP X2 
 WHERE X2.DOCID = Z.DOCIDBOTTOM) PARTNUMBER 
FROM LOOKUP X
INNER JOIN LINKS Z
ON X.DOCID = Z.DOCIDTOP) TB

Answer 1

我发现很难弄清楚你的查询应该做什么。但是，我认为这是等价的：

     SELECT X.INTERNALID, X2.PARTNUMBER 
     FROM LOOKUP X INNER JOIN
          LINKS Z
          ON X.DOCID = Z.DOCIDTOP INNER JOIN
          LOOKUP X2
          ON X2.DOCID = Z.DOCIDBOTTOM;

在同一个表查询中优化一对多关系

1 个答案: