[GitHub] spark pull request #14191: [SPARK-16217][SQL] Support SELECT INTO statement

[wuxianxingkong]

Github user wuxianxingkong commented on a diff in the pull request:

    https://github.com/apache/spark/pull/14191#discussion_r71067768
  
    --- Diff: 
sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBase.g4 ---
    @@ -338,7 +338,7 @@ querySpecification
            (RECORDREADER recordReader=STRING)?
            fromClause?
            (WHERE where=booleanExpression)?)
    -    | ((kind=SELECT setQuantifier? namedExpressionSeq fromClause?
    +    | ((kind=SELECT setQuantifier? namedExpressionSeq (intoClause? 
fromClause)?
    --- End diff --
    
    At first, I modify grammar:
    ![wrong select 
into](https://raw.githubusercontent.com/wuxianxingkong/storage/master/original_select_into.png)
    But it will affect multiInsertQueryBody rule, i.e.:
    ```sql
    FROM OLD_TABLE
    INSERT INTO T1
    SELECT C1
    INSERT INTO T2
    SELECT C2
    ```
    The Syntax tree before adding intoClause is:
    ![right tree 
structure](https://raw.githubusercontent.com/wuxianxingkong/storage/master/original_muliinsert_tree.png)
    After adding intoClause ,the tree will be:
    ![wrong tree 
structure](https://raw.githubusercontent.com/wuxianxingkong/storage/master/wrong_multiinserttree.png)
 This is because INSERT is a nonreserved keyword and matching strategy of antlr.
    One of the ways I can think of is to change grammar like this:
    ![one 
way](https://raw.githubusercontent.com/wuxianxingkong/storage/master/solve_way.png)
    This can solve the problem because antlr parser chooses the alternative 
specified first.
    By the way, the grammar now can support "SELECT 1 INTO newtable" now.
    But this will cause confusion about querySpecification rule because of the 
duplication. Is there any way to solve this problem?Thanks.


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