Show filter condition

[apstndb]

Currently, Seek Condition/Residual Condition predicates of FilterScan operator are shown but Condition predicate of Filter operator is not shown.
Showing them helps to understand query executions.

This PR fix to show Filter's Condition.

Note: It adds testdata directory which contains QueryPlan as JSON.

Before

> EXPLAIN SELECT s.LastName FROM (SELECT s.LastName FROM Singers AS s WHERE s.FirstName LIKE 'A%' LIMIT 3) s WHERE s.LastName LIKE 'Rich%';
+----+-----------------------------------------------------------------+
| ID | Query_Execution_Plan (EXPERIMENTAL)                             |
+----+-----------------------------------------------------------------+
|  0 | Serialize Result                                                |
|  1 | +- Filter                                                       |
|  2 |    +- Global Limit                                              |
| *3 |       +- Distributed Union                                      |
|  4 |          +- Local Limit                                         |
|  5 |             +- Local Distributed Union                          |
| *6 |                +- FilterScan                                    |
|  7 |                   +- Index Scan (Index: SingersByFirstLastName) |
+----+-----------------------------------------------------------------+
Predicates(identified by ID):
 3: Split Range: STARTS_WITH($FirstName, 'A')
 6: Seek Condition: STARTS_WITH($FirstName, 'A')

1 rows in set (0.02 sec)

After

> EXPLAIN SELECT s.LastName FROM (SELECT s.LastName FROM Singers AS s WHERE s.FirstName LIKE 'A%' LIMIT 3) s WHERE s.LastName LIKE 'Rich%';
+----+-----------------------------------------------------------------+
| ID | Query_Execution_Plan (EXPERIMENTAL)                             |
+----+-----------------------------------------------------------------+
|  0 | Serialize Result                                                |
| *1 | +- Filter                                                       |
|  2 |    +- Global Limit                                              |
| *3 |       +- Distributed Union                                      |
|  4 |          +- Local Limit                                         |
|  5 |             +- Local Distributed Union                          |
| *6 |                +- FilterScan                                    |
|  7 |                   +- Index Scan (Index: SingersByFirstLastName) |
+----+-----------------------------------------------------------------+
Predicates(identified by ID):
 1: Condition: STARTS_WITH($LastName, 'Rich')
 3: Split Range: STARTS_WITH($FirstName, 'A')
 6: Seek Condition: STARTS_WITH($FirstName, 'A')

1 rows in set (0.01 sec)

[yfuruyama]

This should be t.Fatal as it can't continue the test.

[apstndb]

Fixed in a05abe8

[yfuruyama]

Same to the above.

[apstndb]

Fixed in a05abe8

[yfuruyama]

By the way, what is the reason to have condition child.DisplayName != "Function"? If I understand correctly, Function operator is not visible in our query plan.

[apstndb]

Predicates are subset of Function operators which returns bool so Function are not visible as nodes of the operator tree but needs to be visible as predicates.
Although, there are no return type information in PlanNode so it is whitelisted by the type name of ChildLink which link to the Function operator as predicates.

Currently, I don't yet see a child link like which type is *Condition and child is not Function so only ChildLink.type is needed information to distinguish predicates but I think that to be Function is a necessary condition to be a predicate so I require it explicitly.

[apstndb]

Extract isPredicate function in 876f838

[yfuruyama]

Ah that makes sense. Thank you for clarifying it!

[yfuruyama]

Looks good!

[yfuruyama]

LGTM!