sql - How range queries identified attribute name in analytic function oracle? -

prototype of range windows defined below

function( ) on (partition <expr1> order <expr2> range between <start_expr> , <end_expr>) or function( ) on (partition <expr1> order <expr2> range [<start_expr> preceding or unbounded preceding] 

it's not mentioned range given attributes(x) how parser/evaluation engine identifies attributes(x) .

select deptno, empno, sal, count(*) on (partition deptno order sal range between unbounded preceding , (sal/2) preceding) cnt_lt_half, count(*) on (partition deptno order sal range between (sal/2) following , unbounded following) cnt_mt_half emp order deptno, sal; 

in above sql query range applied on employee salary .how parser/evaluation engine identifies range given sal. since no mentioned sal between value .

partition deptno defines groups

order sal defines order of rows in each group

range between [start] , [end] defines a window each row in each group. cannot specify clause unless have specified order by. window boundaries defined range clause let specify 1 expression in order by.

range specifies window logical offset. looks @ order expression(s) determine window.

in example range set each row. each row determines rows used analytic function. these rows begining of group max row having salary <= salary of current row (as can see impossible determine without order by, that's why windowing clause requires ordering).

id  depno  sal 1   1       5 2   1       6 3   1       10    4   2       1    5   2       2    6   2       5    7   2       6 

for row id = 6 window

id  depno  sal 4   2       1   -- unbounded preceding (start first row in group: depno = 2) 5   2       2   -- row has salary < salary of row id=6 (2 < 5/2)