help needed for sql grammar

[g naveena <naveena08@yahoo.co.in>]

hi,

   I am trying to write grammar for SQL.
   I went through OQL grammar which is given in the
site. i have some doubts in it
in the production like

expr =     expr_restricted |

     {identifier} identifier |
     ({literal} literal ) |
     ({star} star ) |
     ({long_param} dollar long_literal ) |
     ({named_param} dollar identifier ) |

     ({select} select_x ) |
     ({nested} bracket_l query bracket_r) |


having_clause =
     (having expr) |
     {tmp} having expr_restricted ;

why only some of them are enclosed within the brackets
while others are not

what is the significance of the enclosing brackets
how does it change

thanks in advance

G.Naveena
System Designer
Centre for Good Governance
Hyderabad
India


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