Major Description
Suggesting to separate the ANTLR grammar defined in `SqlBase.g4` into separate parser `SqlBaseParser.g4` and lexer `SqlBaseLexer.g4`.
Benefits:
Gain more flexibility when implementing new SQL features
The current ANTLR grammar definition is given as a mixed grammar in the `SqlBase.g4` file.
By separating the lexer and parser, we will be able to use the full power of ANTLR parser and lexer grammars. e.g. lexer mode. This will give us more flexibility when implementing new SQL features.
The code is more clean.
Having parser and lexer in different files also keeps the code more explicit about which is the parser and which is the lexer.
