Main   Products   Offshore Outsourcing   Customers   Partners   ContactUs  
JDBC Databases
  HXTT Access v5.2
  Buy Now
  HXTT Cobol v2.1
  HXTT DBF v5.2
  HXTT Excel v4.2
  HXTT Paradox v5.2
  HXTT Text(CSV) v5.2
  HXTT XML v1.2
Offshore Outsourcing
Oracle Data Import/Export
DB2 Data Import/Export
Sybase Data Import/Export
Free Resources
  Firewall Tunneling
  Search Indexing Robot
  Conditional Compilation
  Password Recovery for MS Access
  Password Recovery for Corel Paradox
  Checksum Tool for MD5
  Character Set Converter
  Pyramid - Poker of ZYH
Hongxin Technology & Trade Ltd. of Xiangtan City (abbr, HXTT)

SQL query anomaly
Philippe Gervaise
2016-09-02 13:56:51.0

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 :

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.

Search Key   Search by Last 50 Questions


Address: 9 Station Rd., Xiangtan City, Hunan Province, P.R. China
Postcode: 411100
Phone: (86)731-58225727
Fax: (86)731-58225727
Copyright © 1999-2011 Hongxin Technology & Trade Ltd. | All Rights Reserved. | Privacy | Legal | Sitemap