mysql - An explanation for BNF rule -

i'm investigating mysql's sql parser @ moment.

and here interesting thing have noticed , cannot explain:

(in sql_yacc.yy)

predicate:         ...         | bit_expr between_sym bit_expr and_sym predicate           {             $$= new (yythd->mem_root) item_func_between($1,$3,$5);             if ($$ == null)               mysql_yyabort;           } 

the same on expression syntax page:

predicate:   ...   | bit_expr [not] between bit_expr , predicate 

that means that

foo between 1 , bar between 1 , 2 

query syntactically correct, while makes no sense @ all.

my question: used for? miss if used

bit_expr [not] between bit_expr , bit_expr 

instead?

lol (not lol anymore actually)

this query executes without errors:

select * users id between 1 , id between 1 , 10; // returns row id = 1  select * users id between 2 , id between 2 , 10; empty set (0.00 sec) 

(update added here) ... , is expected.

presumably converts second expression straight 0 or 1 , uses operand.

upd:

i've filed bug - http://bugs.mysql.com/bug.php?id=69208

it's not expected syntax @ all

upd 2: looks it's minor typo doesn't change parser behaviour @ (well, clear makes unnoticeable slower common between expression).

your analysis correct:

foo between 1 , bar between 1 , 2 

is parsed as:

foo between 1 , (bar between 1 , 2) 

and second (parenthesized) predicate presumably evaluate either 0 or 1 (for false or true). therefore, if bar not between 1 , 2, set of selected values foo empty (because foo between 1 , 0 shorthand foo >= 1 , f <= 0 , there no values true, allowing nulls). contrariwise, if bar between 1 , 2, set of selected values foo set `foo1 equals 1.

and alternative question "what lose if replaced 'predicate' term 'bit_expr'?" might "would gain if replaced 'bit_expr' 'predicate'?"

without careful scrutiny of complete grammar (or, @ least, scrutiny of parts referenced bit_expr , predicate, , possibly review of places bit_expr , predicate used), hard know answer either question.