Takes 4 parameters, FieldBase, Left, Comparison, Right
All Records in the Query that evaluate to True based on the Comparison Operator will be kept, all others will be discared. Note that the Comparison is a parameter, and as such, may be passed from the Top Query or be a quoated text string literal.
Alternatively, if both Comparison and Right are blank, then all Records in the Query where the Field referenced in Left is not blank (True) will be kept. This logic may be inversed by using Not followed by a space in front of the Field name. Note that this form is faster / more efficient than using a Comparison.
FieldBase, Left, Comparison, Right
[WorkWith], Left, Comparison, Right
FieldBase, Left, [""], [""]
[WorkWith], Left, [""], [""]
KeepIf "MemTab.Person.", "Firstname", "=", "`Bob"