AllyKaz commented on issue #16841:
URL: 
https://github.com/apache/shardingsphere/issues/16841#issuecomment-1218061362

   Having looked at this, I don't think there's an issue to solve. The double 
parsing is the consequence of an optimisation that first attempts to parse with 
a faster, but less powerful algorithm (SLL), that either returns a correct 
parse tree or throws an error which may, or may not, indicated that there's a 
actual syntax error or it requires the more powerful LL algorithm. 
   
   Consequently, given the use of POSITION is a syntax error, the double 
parsing is a necessary and unavoidable part of the optimisation. Maybe the 
optimisation could be improved on, but I don't see this behaviour as 
necessitating that, and that's probably a bit much for good first issue.
   
   [https://tomassetti.me/improving-the-performance-of-an-antlr-parser/](url) 


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