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Does order of the columns in an Index definition for a table in a database has any effect on the performance?
for e.g. are these two queries different ?
CREATE INDEX xxx ON tablex(col1,col2)
CREATE INDEX xxx ON tablex(col2,col1)
what about the in case that I use a BTREE index?
I am using Mysql.
thanks
Yes it does make a difference. An index on (col1, col2) can serve queries that only require an index on col1 but it cannot be used for queries that require only col2.