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Cardinality of integers
Posted by: David Stevenson
Date: March 20, 2006 05:20AM

I have an integer column 'DistinctTopicWordID' which I index using a non-unique index. The column data is definitely not unique, and neither is it a single value - there is a fair spread of over 24000 values in the 500000-odd rows. However, the cardinality always shows 1 (see below). Why is this. Am I missing something basic?

Brain-waves would be appreciated.
Stevod

/*Column Information For - results.ttrimmedrelatedwords*/
---------------------------------------------------------

Field Type Collation Null Key Default Extra Privileges Comment
------------------- ---------------- --------------- ------ ------ ------- ------ ------------------------------- -------
topicword varchar(45) utf8_general_ci NO select,insert,update,references
peakpercentword float (NULL) NO 0 select,insert,update,references
RelatedWordID int(10) unsigned (NULL) NO 0 select,insert,update,references
divpercentword float (NULL) YES (NULL) select,insert,update,references
DBID int(10) unsigned (NULL) YES (NULL) select,insert,update,references
URL varchar(255) utf8_general_ci NO select,insert,update,references
DistinctTopicWordID int(10) unsigned (NULL) NO MUL select,insert,update,references

/*Index Information For - results.ttrimmedrelatedwords*/
--------------------------------------------------------

Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment
-------------------- ---------- ------------------- ------------ ------------------- --------- ----------- -------- ------ ------ ---------- -------
ttrimmedrelatedwords 1 DistinctTopicWordID 1 DistinctTopicWordID A 1 (NULL) (NULL) BTREE

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Cardinality of integers
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