Macro

Summary

A macro that performs iteration.

Package

cl

Signature

loop {for|as} var
 [type-spec] 

     being {the|each}{records|record}

     {in|of} query-expression
 => result

Arguments

var

A variable.

query-expression

A SQL query-statement

Values

result

An object.

Description

The Common Lisp loop macro has been extended with a clause for iterating over query results. This extension is available only when the SQL interface has been loaded. See The SQL Package. For a full description of the rest of the Common Lisp loop facility, see the Common Lisp Hyperspec.

Each iteration of the loop assigns the next record of the table to the variable var. The record is represented in Lisp as a list. Destructuring can be used in var to bind variables to specific attributes of the records resulting from query-expression. In conjunction with the panoply of existing clauses available from the loop macro, the new iteration clause provides an integrated report generation facility.

Example

This extended loop example, on each record returned as a result of the query, binds name, finds the salary (if any) from an associated hash-table, and for salaries greater than 20000: increments a count, accumulates the salary, and prints the details. Finally, the average salary is printed.

(loop

  for (name) being each record in

  [select [ename] :from [emp]]

  as salary = (gethash name *salary-table*)

  initially (format t "~&~20A~10D" 'name 'salary)

  when (and salary (> salary 20000))

   count salary into salaries

   and sum salary into total

   and do (format t "~&~20A~10D" name salary)

  else

   do (format t "~&~20A~10A" name "N/A")

  finally

   (format t "~2&Av Salary: ~10D" (/ total salaries)))

See also

do-query
map-query
query
select