Count(*) – Explaining different behaviour in Joins

Observations :  Count(1) or Count(*) – This is never expanded on each column individually so will work perfectly fine on complete data.  Count(1) is more optimized then Count(*) Count(source.*) – source represents “Left table” of “Left Outer Join”: This will be evaluated as Count(source.col1, source.col2, …. source.colN ) So, if any column has NULL, then the complete row … Read more