zeroflag opened a new pull request #1228:
URL: https://github.com/apache/hive/pull/1228
## NOTICE (work in progress)
### Pushing the TopNKey operator through PK-FK inner joins.
Example:
Customer table:
ID (PK) | LAST_NAME
-- | --
1 | Robinson
2 | Jones
3 | Smith
4 | Heisenberg
Order table:
CUSTOMER_ID (FK) | AMOUNT
-- | --
1 | 100
1 | 50
2 | 200
3 | 30
3 | 40
#### Requirements for doing TopN Key pushdown.
* The PRIMARY KEY constraint on Customer.ID that forbids NULL and duplicate
values.
* The NOT_NULL constraint on Order.CUSTOMER_ID that forbids NULL values.
* Plus the FOREIGN KEY constraint between Customer.ID and Order.CUSTOMER_ID
ensures that exactly one row exists in the Customer table for any given row in
the Order table.
In general if the first n of the order by columns are coming from the child
table (FK) then we can copy the TopNKey operator with the first n columns and
put it before the join. If all columns are coming from the child table we can
move the TopNKey operator without keeping the original.
```
SELECT * FROM Customer, Order
WHERE Customer.ID = Order.CUSTOMER_ID
ORDER BY Order.AMOUNT, [Order.*], [Customer.*] LIMIT 3;
```
Result:
CUSTOMER.ID (PK) | CUSTOMER.LAST_NAME | ORDER.AMOUNT
-- | -- | --
3 | Smith | 30
3 | Smith | 40
1 | Robinson | 50
1 | Robinson | 100
2 | Jones | 200
Plan
```
Top N Key Operator
sort order: +
keys: ORDER.AMOUNT, [ORDER.*]
top n: 3
Select Operator (Order)
[...]
Join
[...]
Top N Key Operator
sort order: +
keys: ORDER.AMOUNT, [ORDER.*], [Customer.*]
top n: 3
```
#### Implementation notes
PkFk join information is extracted on the calcite side and it is attached
(child table index & name) to the AST as a query hint.
At the physical plan level we make use of this information to decide if we
can push through the topn key operator. We also need to get the origins of the
columns (in the order by) to see if they're coming from the child table.
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