Looking at how people are using COUNT(*) and COUNT(col) it looks like most of them think they are synonyms …=latin1 mysql> select count(*) from fact; +———-+ | count(*) | +———-+ | 7340032 | +———-+ 1 row in set (0.00 sec) mysql> select count(val) from fact; +————+ | count(val) | +————+ | 7216582… also why result is different for the second query. So COUNT(*) and COUNT(col) queries not only could have substantial performance performance differences…
Post: A common problem when optimizing COUNT()
September 20, 2008 By 18 Comments
…) count the number of rows 2) count the number of values. Sometimes, but not always, these are the same thing. COUNT(*) always counts the number of rows in the result. If you write COUNT(col1) it counts the number of times… to them: select count(col1) from table; — COUNT_COL_OK Alas, there is a lot of misinformation on the web about COUNT(), so it…
Comment: COUNT(*) vs COUNT(col)
April 25, 2007 By 41 Comments
… find that, with a judicious choice of (col), count(col) may actually be a lot faster than count(*). Consider this example (restarting mysql each… 0 restart mysql and check the count of (rajid): mysql> select count(rajid) from wp_comments; +————–+ | count(rajid) | +————–+ | 230120 | +————–+ 1 row in set…
Comment: Terms of Use
February 26, 2008 By 17 Comments
… MySQL and other ‘skills’. I personally expected that COUNT(col) should be faster that COUNT(*) in the first place. Nice to read that… 
The article can be found at: http://codequest.nl/article/count_ster_vs_count_kolomnaam Thanks again!
Comment: COUNT(*) vs COUNT(col)
October 1, 2009 By 41 Comments
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Comment: COUNT(*) vs COUNT(col)
September 12, 2008 By 41 Comments
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Comment: COUNT(*) vs COUNT(col)
May 20, 2010 By 41 Comments
[...] Performance Blog Post:COUNT(*) vs COUNT(col) Reference: [...]
Post: Getting around optimizer limitations with an IN() list
January 9, 2010 By 9 Comments
… 60 AND col_a = ‘set1′; +———-+ | count(*) | +———-+ | 1 | +———-+ 1 row in set (0.00 sec) SELECT count(*) FROM coordinates FORCE INDEX (x_y_col_a) WHERE x BETWEEN 30 and 40; +———-+ | count(*) | +———-+ | 1664 | +———-+ 1 row…
Post: Quickly preloading Innodb tables in the buffer pool
May 1, 2008 By 9 Comments
… pool pretty efficiently by using something like SELECT count(*) FROM tbl WHERE non_index_col=0 This works relatively well (though can… Indexes preloaded you can use something like SELECT count(*) from tbl WHERE index_col like “%0%” for each index. Only one such… stored columns you can use similar query: SELECT count(*) from tbl WHERE blob_col like “%0%”. Note if you preloading BLOB/TEXT…
Post: Beware the Innodb Table Monitor
November 29, 2011 By 2 Comments
… to use the Innodb Table monitor to diagnose an Index count mismatch error a customers found in their mysqld.err log… 0; REF_NAME: DATA_VARCHAR DATA_ENGLISH len 0; N_COLS: DATA_INT len 4; DB_ROW_ID: DATA_SYS prtype…_TRX_ID DB_ROLL_PTR FOR_NAME REF_NAME N_COLS INDEX: name FOR_IND, id 0 12, fields 1/2…
