Next: Aggregate functions, Previous: Builtin functions, Up: Expressions [Contents][Index]
Aggregate expressions ( <aggr_expr>s) are
currently used exclusively by the LOGS
statement. They represent an
expression with a given function applied to the aggregate of all
(dynamic) instances of that expression.
<aggr_expr>s take one of four forms:
<aggr_expr>  ::=  [ EACH ]
<expr> 
  THE
<expr> 

  THE
<aggr_func> [ AND THE <aggr_func>]*
[ OF [ THE ]]
<expr> 

 
A HISTOGRAM OF [ THE ] <expr> 
(In the above, <expr> refers to an arithmetic expression defined in Arithmetic expressions and <aggr_func> refers to one of the functions defined in Aggregate functions.)
The first form does not summarize <expr>; every individual instance of <expr> is utilized. The second form asserts that <expr> is a constant (i.e., all values are identical) and utilizes that constant.^{13} The third form applies each <aggr_func> to the set of all values of <expr> and utilizes the result of that function. The fourth form produces a histogram of all values of <expr>, i.e., a list of {unique value, tally} pairs, sorted by unique value.
Scott Pakin, pakin@lanl.gov