Re: Specifying multiple WHERE options within a group?

[Jay Pipes]

Callum,

I'm assuming that the TrackingActions table is simply two fields, Action and UserID (something like VARCHAR(30), INT). If so, it would be highly beneficial to this query to add a reverse Primary Key index in the form:

UNIQUE INDEX (UserID, Action)

as well as the PRIMARY KEY (Action, UserID)

Both these indexes will be used in the above query. The outermost TrackingActions SELECT would use the PRIMARY KEY index, while the self joins would use the UNIQUE INDEX on the reversed PRIMARY KEY.

Jay Pipes
Community Relations Manager, North America, MySQL Inc.

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