Improve EXPLAIN SYNTAX with ASTSelectWithUnionQuery

[ucasfl]

I hereby agree to the terms of the CLA available at: https://yandex.ru/legal/cla/?lang=en

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Improve EXPLAIN SYNTAX with ASTSelectWithUnionQuery.

Detailed description / Documentation draft:

InterpreterSelectWithUnionQuery normalizes the ASTSelectWithUnionQuery, so we need improve ExplainAnalyzedSyntaxVisitor in InterpreterExplainQuery to show the correct syntax.

For example:

before

EXPLAIN SYNTAX                                                                                                                            [1/1807]
SELECT 1                                                                                                                                          
UNION ALL
(
    SELECT 1
    UNION ALL
    (
        SELECT 1
        UNION ALL
        SELECT 1
    )
    UNION ALL
    SELECT 1
)

Query id: c542fb59-4fe7-4c9d-93c4-b0e34528f564

┌─explain───────────┐
│ SELECT 1          │
│ UNION ALL         │
│ (                 │
│     SELECT 1      │
│     UNION ALL     │
│     (             │
│         SELECT 1  │
│         UNION ALL │
│         SELECT 1  │
│     )             │
│     UNION ALL     │
│     SELECT 1      │
│ )                 │
└───────────────────┘

13 rows in set. Elapsed: 0.022 sec.  

EXPLAIN SYNTAX                                                                                                                                    
SELECT 1                                                                                                                                          
UNION ALL
(
    SELECT 1
    UNION DISTINCT
    (
        SELECT 1
        UNION ALL
        SELECT 1
    )
    UNION ALL
    SELECT 1
)

Query id: 5f1995c3-8883-4535-b8ab-30ce99b69090

┌─explain────────────┐
│ SELECT 1           │
│ UNION ALL          │
│ (                  │
│     SELECT 1       │
│     UNION DISTINCT │
│     (              │
│         SELECT 1   │
│         UNION ALL  │
│         SELECT 1   │
│     )              │
│     UNION ALL      │
│     SELECT 1       │
│ )                  │
└────────────────────┘

now

EXPLAIN SYNTAX
SELECT 1
UNION ALL
(
    SELECT 1
    UNION ALL
    (
        SELECT 1
        UNION ALL
        SELECT 1
    )
    UNION ALL
    SELECT 1
)

Query id: 3b872702-4558-455c-9a00-e2905288e1f8

┌─explain───┐
│ SELECT 1  │
│ UNION ALL │
│ SELECT 1  │
│ UNION ALL │
│ SELECT 1  │
│ UNION ALL │
│ SELECT 1  │
│ UNION ALL │
│ SELECT 1  │
└───────────┘

9 rows in set. Elapsed: 0.029 sec. 

EXPLAIN SYNTAX
SELECT 1
UNION ALL
(
    SELECT 1
    UNION DISTINCT
    (
        SELECT 1
        UNION ALL
        SELECT 1
    )
    UNION ALL
    SELECT 1
)

Query id: f902ac63-7f88-4439-a316-315de09b3731

┌─explain────────────┐
│ SELECT 1           │
│ UNION ALL          │
│ (                  │
│     SELECT 1       │
│     UNION DISTINCT │
│     SELECT 1       │
│     UNION DISTINCT │
│     SELECT 1       │
│ )                  │
│ UNION ALL          │
│ SELECT 1           │
└────────────────────┘

11 rows in set. Elapsed: 0.038 sec.