coalesce and nvl question

[Simon Windsor]

Hi

Is there a standard postgres method of replacing empty strings.

In Oracle, nvl handles nulls and empty strings, as does ifnull() in
MySQL, but with postgres coalesce only handles null strings.

If, not is the best solution to create a plpgsql function, ie

CREATE FUNCTION isEmpty (character varying, character varying) RETURNS
character varying
AS '
declare
fnRetTrue alias for $1;
fnRetFalse alias for $2;
begin
if fnRetTrue = '' or fnRetTrue is not null then
return fnRetTrue;
else
return fnRetFalse;
end if;
end;
'
LANGUAGE plpgsql;

Thanks

Simon

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[Mike Mascari]

Simon Windsor wrote:

Hi

Is there a standard postgres method of replacing empty strings.

In Oracle, nvl handles nulls and empty strings, as does ifnull() in
MySQL, but with postgres coalesce only handles null strings.

If, not is the best solution to create a plpgsql function, ie

CREATE FUNCTION isEmpty (character varying, character varying) RETURNS
character varying

This all depends upon what you mean by handle. Do you want to treat
empty strings as NULL or NULL as empty strings? As you said, you can
treat NULL as empty strings using COALESCE:

SELECT COALESCE(x, '');

You can treat empty strings as NULL

SELECT NULLIF(x, '');

But I'd guess most on this list are wondering why you want to equate
an empty string with NULL, as they have two distinct meanings.
Oracle's treatment of empty strings as NULL is world-renowned for
being insane...

HTH

Mike Mascari

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[Simon Windsor]

Hi

I understand that null and '' are different, and MySQL and Oracle
functions are confusing, but my question was not about replacing NULL
but replacing Empty strings. These are handled in MySQL/Oracle by the
same functions that do NULL checks.

Is there a standard function in Postgres that replaces Empty strings, as
against a NULL value.

Simon

On Wed, 2004-06-23 at 18:05, Mike Mascari wrote:

Simon Windsor wrote:

Hi

Is there a standard postgres method of replacing empty strings.

In Oracle, nvl handles nulls and empty strings, as does ifnull() in
MySQL, but with postgres coalesce only handles null strings.

If, not is the best solution to create a plpgsql function, ie

CREATE FUNCTION isEmpty (character varying, character varying) RETURNS
character varying

This all depends upon what you mean by handle. Do you want to treat
empty strings as NULL or NULL as empty strings? As you said, you can
treat NULL as empty strings using COALESCE:

SELECT COALESCE(x, '');

You can treat empty strings as NULL

SELECT NULLIF(x, '');

But I'd guess most on this list are wondering why you want to equate
an empty string with NULL, as they have two distinct meanings.
Oracle's treatment of empty strings as NULL is world-renowned for
being insane...

HTH

Mike Mascari

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Email: si***********@cornfield.org.uk
Tel: [phone]
Mob: [phone]
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[Doug McNaught]

Simon Windsor <si***********@cornfield.org.uk> writes:

Hi

I understand that null and '' are different, and MySQL and Oracle
functions are confusing, but my question was not about replacing NULL
but replacing Empty strings. These are handled in MySQL/Oracle by the
same functions that do NULL checks.

Is there a standard function in Postgres that replaces Empty strings, as
against a NULL value.

I don't think so, but you could use a CASE clause for this.

-Doug

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[Bruno Wolff III]

On Wed, Jun 23, 2004 at 19:10:05 +0100,
Simon Windsor <si***********@cornfield.org.uk> wrote:

Hi

I understand that null and '' are different, and MySQL and Oracle
functions are confusing, but my question was not about replacing NULL
but replacing Empty strings. These are handled in MySQL/Oracle by the
same functions that do NULL checks.

Is there a standard function in Postgres that replaces Empty strings, as
against a NULL value.

Something like the following may suit your purposes:
coallesce(nullif(inputstring,''), 'replacement value')

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[Simon Windsor]

Hi

Thanks, I should have thought of that myself!

Simon
On Wed, 2004-06-23 at 19:43, Bruno Wolff III wrote:

On Wed, Jun 23, 2004 at 19:10:05 +0100,
Simon Windsor <si***********@cornfield.org.uk> wrote:

Hi

I understand that null and '' are different, and MySQL and Oracle
functions are confusing, but my question was not about replacing NULL
but replacing Empty strings. These are handled in MySQL/Oracle by the
same functions that do NULL checks.

Is there a standard function in Postgres that replaces Empty strings, as
against a NULL value.

Something like the following may suit your purposes:
coallesce(nullif(inputstring,''), 'replacement value')

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