[GitHub] gatorsmile commented on issue #23276: [SPARK-26321][SQL] Split a SQL in correct way

[GitBox <gi...@apache.org>]

gatorsmile commented on issue #23276: [SPARK-26321][SQL] Split a SQL in correct way
URL: https://github.com/apache/spark/pull/23276#issuecomment-446476683
 
 
   Let us first update the PR description to explain the problem we want to resolve. Regarding comments, our SQL parser follows PostgreSQL. You can read SqlBase.g4 to confirm it. 
   
   ```
   SIMPLE_COMMENT
       : '--' ~[\r\n]* '\r'? '\n'? -> channel(HIDDEN)
       ;
   
   BRACKETED_EMPTY_COMMENT
       : '/**/' -> channel(HIDDEN)
       ;
   
   BRACKETED_COMMENT
       : '/*' ~[+] .*? '*/' -> channel(HIDDEN)
       ;
   ```
   
   In PostgreSQL doc: https://www.postgresql.org/docs/9.4/sql-syntax-lexical.html
   
   > A comment is a sequence of characters beginning with double dashes and extending to the end of the line, e.g.:
   ```
   -- This is a standard SQL comment
   ```
   > Alternatively, C-style block comments can be used:
   ```
   /* multiline comment
    * with nesting: /* nested block comment */
    */
   ```
   > where the comment begins with /* and extends to the matching occurrence of */. These block comments nest, as specified in the SQL standard but unlike C, so that one can comment out larger blocks of code that might contain existing block comments.
   
   > A comment is removed from the input stream before further syntax analysis and is effectively replaced by whitespace.

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