Question

我有两个表：newparts，storedparts

我将存储部件中未喷射的新部件插入到已存储的部件中：

SQL_String = "INSERT INTO storedparts " & _
             "SELECT newparts.* " & _
             "FROM storedparts " & _
             "RIGHT JOIN newparts ON (storedparts.identifier = newparts.identifier) AND (storedparts.timeStamp = newparts.timeStamp) " & _
             "WHERE ((storedparts.AutoID) Is Null);"

到目前为止，此工作正常。现在的问题：Table storedparts变得如此之大，以至于程序对于连接过程来说太长了。我的解决方案：只是将新部件与存储部件的所有部分进行比较，而不仅仅是对不超过4天的部件进行比较......我尝试了这样的子查询，但我无法运行它

SQL_String = "INSERT INTO storedparts " & _
             "SELECT newparts.* " & _
             "FROM storedparts (WHERE storedparts.timestamp > Now() - 4) " & _
             "RIGHT JOIN newparts ON (storedparts.identifier = newparts.identifier) AND (storedparts.timeStamp = newparts.timeStamp) " & _
             "WHERE ((storedparts.AutoID) Is Null);"

感谢任何帮助。

Answer 1

您可以在join语句之后添加where子句，看看它是否提高了查询的性能。否则尝试一下，看看它是否有效

SQL_String = "INSERT INTO storedparts " & _
             "SELECT newparts.* " & _
             "FROM ( SELECT * FROM storedparts WHERE 
              storedparts.timestamp > DateAdd ( 'd', -4, Now()) )sparts" & _
             "RIGHT JOIN newparts ON (sparts.identifier = newparts.identifier) AND 
             (sparts.timeStamp = newparts.timeStamp) " & _
             "WHERE ((sparts.AutoID) Is Null);"

Answer 2

如果你的表有索引，这不会有问题。

CREATE INDEX ndx_sp_identifier ON storedparts (identifier);
CREATE INDEX ndx_np_identifier ON newparts (identifier);

然后我建议你把你的查询改成像@jarlh指出的那样。

INSERT INTO storedparts 
SELECT newparts.* 
FROM newparts
LEFT JOIN storedparts 
ON newparts.identifier = storedparts.identifier
AND newparts.timeStamp = storedparts.timeStamp
WHERE storedparts.AutoID Is Null;

MS ACCESS SQL加入子查询

2 个答案: