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Hongxin Technology & Trade Ltd. of Xiangtan City (abbr, HXTT)

HXTT ACCESS
SQL query anomaly
Philippe Gervaise
2016-09-02 13:56:51.0
Hi,

I got an anomaly concerning time execution with a query. Take this query :

SELECT TOP 1 * FROM t2 LEFT JOIN t1 ON t1.t1_id = t2.t1_id WHERE t1.t1_id IS NULL

It took 42 minutes.

t1 : 47351 records, only one column and no primary key
t2 : 162825 records, two columns and a composed primary key with the 2 columns (the primary key on two columns seems the problem)

On Access the query took 0,3s.

A test database can be downloaded here :

https://penelope827-my.sharepoint.com/personal/p_gervaise_penelope_fr/_layouts/15/guestaccess.aspx?guestaccesstoken=jdCA0rorTzP4kY7GtdVtZSinmh63B94fBJs7jp8bAoU%3d&docid=07f43cdc28c624156b3751358a6d281f9&rev=1&expiration=2016-10-02T20%3a45%3a50.000Z

Note : I simplified the query and the database. With our database it took a lot longer and it's reading more than 2 Terabytes !
Re:SQL query anomaly
HXTT Support
2016-09-03 22:11:19.0
2016-09-04 fixed a speed bug on LEFT JOIN when left table has a component index expression.

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