grammar

    Query grammar

    <query>             ::= select <resultcolumns> [ from <source> ] [where <expr> ] [group by <orderingterms>] [order by <orderingterms> [having <expr>]] [limit <digit> [offset <digit ]] ";"

    <resultcolumns>     ::= <resultcolumn> | <resultcolumn>,<resultcolumns>

    <resultcolumn>      ::= * | <expr> [ as <colname> ]

    <colname>           ::= <identifier>

    <source>            ::= tablename
    
    <identifier>        ::= letter {letter|digit}

    <orderingterms>     ::= <orderingterm> {, <orderingterm>}

    <orderingterm>      ::= <expr> [as <identifier>]

    <digit>             ::= 0-9

    <letter>            ::= a-zA-Z

    <expr>              ::= <literal> |
                            <colname> |
                            <unary-op> <expr> |
                            <expr> <binary-op> <expr> |
                            <function> (<expr>|*) |
                            ( <expr> ) 

    <literal>           ::= "'"{ any_character }"'" | <number>

    <number>		::= <digit> {<digit>} [ "." {<digit>}] | "." <digit> {<digit>} ["e" [+|-] <digit> {<digit>} ]

    <unary-op>          ::= "+" | "-" | "~" | NOT

    <binary-op>         ::= "||" | "*" | "/" | "%" | "+" | "-" | "<<" | ">>" | "&" | "|" | "<" | "<=" | ">" | ">=" | "=" | "==" | "!=" | "<>" | IS | IS NOT | AND | OR

    <function>          ::= COUNT | AVG | SUM | MIN | MAX | TRUNCATE | RSPLIT | IF | NAME | TRIM | LOWER | STDEV