//----------------------------------------------------------------------------
// The condition for a self-cancelling delta
// (SYS_MAV.cnts IS NULL AND SYS_DELTA.cnts = 0)
// If the MAV has no GROUP BY clause, the condition is:
// (SYS_MAV.cnts = 0 AND SYS_DELTA.cnts = 0)
//----------------------------------------------------------------------------
ItemExpr *MavRelRootBuilder::buildSelfCancelingDeltaPredicate()
{
// Find the MAV column name for COUNT(*).
const NAString& countStarColName = mavCols_[posOfCountStar_]->getColName();
ItemExpr *mavCountStarCondition = NULL;
ItemExpr *mavCountStarName = new(heap_)
ColReference(new(heap_) ColRefName(countStarColName, mavCorrName_));
if (isMavWithoutGroupBy())
{
// (SYS_MAV.cnts = 0)
mavCountStarCondition = new(heap_)
BiRelat(ITM_EQUAL, mavCountStarName, new(heap_) SystemLiteral(0));
}
else
{
// (SYS_MAV.cnts IS NULL)
mavCountStarCondition = new(heap_)
UnLogic(ITM_IS_NULL, mavCountStarName);
}
// (mavCountStarCondition AND SYS_DELTA.cnts = 0)
ItemExpr *selfCancelCondition = new(heap_)
BiLogic(ITM_AND,
mavCountStarCondition,
new(heap_) BiRelat(ITM_EQUAL,
new(heap_) ColReference(new(heap_)
ColRefName(countStarColName, deltaCorrName_)),
new(heap_) SystemLiteral(0)));
ItemExpr *notSelfCancelingDeltaPredicate =
new(heap_) UnLogic(ITM_NOT, selfCancelCondition);
notSelfCancelingDeltaPredicate->setSelectivityFactor(1.0);
return notSelfCancelingDeltaPredicate;
} // MavRelRootBuilder::buildSelfCancelingDeltaPredicate()
