Thread: Trigger function failure

Trigger function failure

From

Michael Rowan

Date:

07 March 2016, 09:43:19

I have a trigger function problem that threatens to cause my early demise. Please someone help an absolute novice.

I have two tables, invoice and invline, with the usual functions.

Table invoice has a column for the total of debit lines, and a column for the total of credit (payment) lines. The function is triggered by any change in inv.gross

The ERROR occurs if there are no invline found by either summing part, where we set dr_total or cr_total.

If I change "sum" to "count" it works as expected, returning 0.00

--THE FUNCTION

UPDATE invoice SET

invoice.cr_total = (

SELECT

sum(invline.gross)

FROM invline

WHERE invline.type > 4 AND invline.invoice_id = 200003

)

invoice.dr_total = (

SELECT

sum(invline.gross)

FROM invline

WHERE invline.type <5 AND invline.invoice_id = 200003

)

WHERE invoice.id = 200003;

--TEST

select invoice.dr_total, invoice.cr_total from invoice where invoice.id=200003

---------------------------------------------------------------------------------------------

ERROR: null value in column "po_cr_total" violates not-null constraint

Anyone?

Mike

Re: Trigger function failure

From

Fábio Moreira

Date:

07 March 2016, 09:50:35

Hi Michael,

From http://www.postgresql.org/docs/current/static/functions-aggregate.html:

It should be noted that except for count, these functions return a null value when no rows are selected. In particular, sum of no rows returns null, not zero as one might expect, and array_agg returns null rather than an empty array when there are no input rows.

(I’m not sure, but I think that’s actually required behavior from the SQL specification.)

This explains why your query works with COUNT(): that function *is* guaranteed to return 0 when run over an empty set.

You can fix that by wrapping COALESCE() call around your subselect: write

COALESCE((SELECT …), 0)

instead of

(SELECT …)

[]s, Fábio.

On Mon, Mar 7, 2016 at 3:43 PM, Michael Rowan <michael.rowan3@gmail.com> wrote:

I have a trigger function problem that threatens to cause my early demise. Please someone help an absolute novice.

I have two tables, invoice and invline, with the usual functions.

Table invoice has a column for the total of debit lines, and a column for the total of credit (payment) lines. The function is triggered by any change in inv.gross

The ERROR occurs if there are no invline found by either summing part, where we set dr_total or cr_total.
If I change "sum" to "count" it works as expected, returning 0.00

--THE FUNCTION
UPDATE invoice SET
invoice.cr_total = (
SELECT
sum(invline.gross)
FROM invline
WHERE invline.type > 4 AND invline.invoice_id = 200003
)
,
invoice.dr_total = (
SELECT
sum(invline.gross)
FROM invline
WHERE invline.type <5 AND invline.invoice_id = 200003
)
WHERE invoice.id = 200003;

--TEST
select invoice.dr_total, invoice.cr_total from invoice where invoice.id=200003

---------------------------------------------------------------------------------------------
ERROR: null value in column "po_cr_total" violates not-null constraint

Anyone?

Mike

Fábio Dias Moreira

Re: Trigger function failure

From

Sándor Daku

Date:

07 March 2016, 12:49:31

On 7 March 2016 at 07:43, Michael Rowan <michael.rowan3@gmail.com> wrote:

I have a trigger function problem that threatens to cause my early demise. Please someone help an absolute novice.

I have two tables, invoice and invline, with the usual functions.

Table invoice has a column for the total of debit lines, and a column for the total of credit (payment) lines. The function is triggered by any change in inv.gross

The ERROR occurs if there are no invline found by either summing part, where we set dr_total or cr_total.
If I change "sum" to "count" it works as expected, returning 0.00

--THE FUNCTION
UPDATE invoice SET
invoice.cr_total = (
SELECT
sum(invline.gross)
FROM invline
WHERE invline.type > 4 AND invline.invoice_id = 200003
)
,
invoice.dr_total = (
SELECT
sum(invline.gross)
FROM invline
WHERE invline.type <5 AND invline.invoice_id = 200003
)
WHERE invoice.id = 200003;

--TEST
select invoice.dr_total, invoice.cr_total from invoice where invoice.id=200003

---------------------------------------------------------------------------------------------
ERROR: null value in column "po_cr_total" violates not-null constraint

Anyone?

Mike

There is a difference between the behaviour of sum and count. Count returns the number of found records(0 in this case) while sum returns the sum of the given expression from the found records. And anything plus null is always null in Postgres.

However you can use the coalesce function which returns its first non-null argument to ensure a non null result.

SELECT

coalece(sum(invline.gross), 0)

FROM invline

WHERE invline.type > 4 AND invline.invoice_id = 200003

invoice.cr_total = coalesce((SELECT

sum(invline.gross)

FROM invline

WHERE invline.type > 4 AND invline.invoice_id = 200003),0)

Regards,

Sándor