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## Novice PL/pgSQL question and example

### Responses

### pgsql-novice by date

At least, I hope this is a Novice question. It sure makes me feel like one! :) Please cc: me directly on replies, as I might miss a reply that goes only to the list. I'm running PostGreSQL 8.3.9 on FreeBSD 6.4-STABLE, but I doubt this is platform-dependent. I'm trying to solve what I'm sure is a common problem in the accounting world. A total cost C has to be split across N different accounts, and C is not necessarily divisible by N. Shares with fractions of pennies are not allowable, and to make the accounting balance, the sum of all the shares has to sum to exactly match the total cost C. It's like splitting a $90 lunch check between 7 people. This PHP code shows the math I'm using, and works great. For clarity to those not familiar with PHP, the &$error in the calc_share function declaration means that parameter $error is passed by reference, not by value. This is necessary because the calc_share function has to keep track of the cumulative error from one share to the next that arises from taking a real number and rounding it to two decimal places. Eventually, the cumulative error will be sufficient to bump a share up or down in value by one penny. I'm using OUT parameters in the PL/pgSQL version to achieve this result. <?php function calc_share( $amount, $shares, &$error ) { $share = $amount / $shares; $result = round( $share + $error, 2 ); $error += $share - $result; return $result; } $amount = 90; $shares = 7; $error_term = 0; $test_sum = 0; for ( $i = 0; $i < $shares; ) { ++$i; $one_share = calc_share( $amount, $shares, $error_term ); print "i = " . $i . " " . $one_share . "\n"; $test_sum = $test_sum + $one_share; } print "sum = " . $test_sum . "\n"; ?> Here is my attempt to implement this in PL/PGSQL. The commented-out UPDATE query is how I would like to use this function in a real-world application (given that there are exactly 7 rows in my table WHERE reference = 'SHARE'). But for now, I'm using the FOR loop and the RAISE NOTICE just to try to see what's going on, and whether my algorithm is working correctly. It's not. --- begin test.sql CREATE OR REPLACE FUNCTION calc_share( cost REAL, N_shares INTEGER, OUT error_term REAL, OUT result REAL ) AS $$ -- When called N consecutive times with identical values of -- COST and N_SHARES, this routine will calculate N shares of a -- value COST and keep track of the error term, so that some shares -- may be one penny higher than other shares, but the sum of all the -- shares will always match the total COST. -- The caller must set error_term to 0 before the first call. DECLARE one_share REAL; result REAL; BEGIN one_share := cost / N_shares; result := ROUND( one_share + error_term, 2 ); error_term := error_term + one_share - result; END; $$ LANGUAGE plpgsql; CREATE OR REPLACE FUNCTION share_costs() RETURNS VOID AS $$ DECLARE error_term REAL; shares INTEGER; i INTEGER; cost REAL; one_share REAL; BEGIN error_term := 0; cost := 90; shares := 7; -- update my_table set amount = calc_share( cost, shares, error_term ) where reference = 'SHARE'; error_term := 0; FOR i IN 1 .. shares LOOP PERFORM calc_share( cost, shares, error_term, one_share ); RAISE NOTICE 'i = %, share = %', i, one_share; END LOOP; END; $$ LANGUAGE PLPGSQL; --- end test.sql I'm trying to invoke this code thusly: $ psql Welcome to psql 8.3.9, the PostgreSQL interactive terminal. Type: \copyright for distribution terms \h for help with SQL commands \? for help with psql commands \g or terminate with semicolon to execute query \q to quit pnwc=> \i test.sql CREATE FUNCTION CREATE FUNCTION pnwc=> \df (trimmed) public | calc_share | record | cost real, n_shares integer, OUT error_term real, OUT result real public | share_costs | void | (1857 rows) pnwc=> select share_costs(); Here I would expect to see 7 rows of output showing the 7 consecutive share values that were calculated. Instead: ERROR: function calc_share(real, integer, real, real) does not exist LINE 1: SELECT calc_share( $1 , $2 , $3 , $4 ) ^ HINT: No function matches the given name and argument types. You might need to add explicit type casts. QUERY: SELECT calc_share( $1 , $2 , $3 , $4 ) CONTEXT: PL/pgSQL function "share_costs" line 15 at PERFORM My novice eyes don't see that the function doesn't exist, or that the types of the parameters are not matched correctly to the function declaration. What am I missing that is preventing this function from working as I would like it to? Thank you. I appreciate your time. Regards, Jim

- Re: Novice PL/pgSQL question and example at 2010-02-08 03:14:46 from James Long
- Re: Novice PL/pgSQL question and example at 2010-02-11 11:31:04 from Jasen Betts

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