Feature: explain AST/syntax statement

[sundy-li]

Summary

Description for this feature.

• explain syntax: output the formatted SQL .

Example:

EXPLAIN SYNTAX
SELECT number
FROM numbers(10)

┌─explain──────────┐
│ SELECT number    │
│ FROM numbers(10) │
└──────────────────┘

• explain ast: output the AST struct.

Example:

explain ast select number from numbers(10);


┌─explain─────────────────────────────────────┐
│ SelectWithUnionQuery (children 1)           │
│  ExpressionList (children 1)                │
│   SelectQuery (children 2)                  │
│    ExpressionList (children 1)              │
│     Identifier number                       │
│    TablesInSelectQuery (children 1)         │
│     TablesInSelectQueryElement (children 1) │
│      TableExpression (children 1)           │
│       Function numbers (children 1)         │
│        ExpressionList (children 1)          │
│         Literal UInt64_10                   │
└─────────────────────────────────────────────┘