Обсуждение: nullif('','') on insert

I need to test whether or not a value is null on
insert. 

Example: insert into table (column) values
nullif('',''));
ERROR: column "column" is of type boolean but
expression is of type text.

It works in MSSQL (probably against not standards) but
nonetheless I need to make it work.

I assume it's returning 'NULL' w/ quotes? I don't know
where to look to alter it. I looked into functions but
all I see is how to write "AS queries" or point to
various snippets. I'd rather just alter the nullif
function. 

Is there a function for this or could someone give me
an example to insert NULL? 

Cheers
Matt

    
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Matt L. wrote:

>I need to test whether or not a value is null on
>insert. 
>
>Example: insert into table (column) values
>nullif('',''));
>ERROR: column "column" is of type boolean but
>expression is of type text.
>  
>
Your problem is that NULL's are typed in PostgreSQL.

Try this:

SELECT NULL;
SELECT NULL::BOOL;
SELECT NULL::BOOL::TEXT;

to see what I mean.  This is an exact illustration of your problem.

>It works in MSSQL (probably against not standards) but
>nonetheless I need to make it work.
>
>I assume it's returning 'NULL' w/ quotes?
>
Nope.  It is returning a text string which is valued at NULL.  It cannot 
convert a text string to a BOOL (even if the string is a NULL) so it 
gives you an error.

> I don't know
>where to look to alter it. I looked into functions but
>all I see is how to write "AS queries" or point to
>various snippets. I'd rather just alter the nullif
>function. 
>  
>
SELECT NULLIF('' = '', TRUE);

Does this work?  You could write a wrapper function if necessary.....

Best Wishes,
Chris Travers
Metatron Technology Consulting

> Your problem is that NULL's are typed in PostgreSQL.
> 
> Try this:
> 
> SELECT NULL;
> SELECT NULL::BOOL;
> SELECT NULL::BOOL::TEXT;
> 
> to see what I mean.  This is an exact illustration of your problem.

Note that in 8.1 he will be able to do:
SELECT NULL::TEXT::INT::BOOL
and get the conversion he wants as long as he sticks to using 0 and 1 to
code for false and true.