The likelihood() function, which should help select a query plan but otherwise be logic-neutral, nevertheless seems to affect results returned by a Left Join, when used as part of the join condition, possibly in other circumstances.
With the following sample data, the two SELECT queries should return the same data, however, they don't: the second query returns a rowcount that would correspond to that of an inner join: drop table if exists Tbl; create temp table Tbl (i int, x, y, z); insert into Tbl values (1,1,1,1), (2,2,2,2), (3,3,3,3), (4,4,4,4); drop table if exists Lkp; create temp table Lkp (i int, bool char); insert into Lkp values (1,'T'), (2,'F'); select count(*) from Tbl left join Lkp on Tbl.i = Lkp.i and Lkp.bool = 'T'; select count(*) from Tbl left join Lkp on likelihood(Tbl.i = Lkp.i, 0.5) and Lkp.bool = 'T';
