[CALCITE-3665] Better estimate join row count when one of the sides is known to be unique

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.21.0
• Component/s: core
• Assignee: Unassigned
• Reporter: Vladimir Sitnikov
• Created: 02/Jan/20 12:43
• Updated: 03/Jan/20 01:00

Description

For instance:
1) select from emp e left join dept d on (e.X = d.id)
This query can't multiply rows, so its row count estimation is rowCount(join.left)

2) select from dept d right join emp e on (d.id = e.X)
This query can't multiply rows, so its row count estimation is rowCount(join.right)

3) select from emp e join dept d on (e.id = d.id)
The rows can't be multiplied here as well

Currently, Calcite estimates the number of rows as left*right which is an overestimation in many cases