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Thread: How to avoid nulls while writing string for dynamic query

How to avoid nulls while writing string for dynamic query

From

"Kumar"

Date:

12 February 2004, 11:30:53

Dear Friends,

Postgres 7.3.4 on RH Linux 7.2.

I wanted to write a dynamic query for insert statement.

create table test(c1 int, c2 varchar)

insert into test(c1, c2) values (1,'Hai1');
insert into test(c1, c2) values (NULL,'Hai2');

so I wrote a function called test_fn()

DECLARE
    sqlstr  VARCHAR(100);
     rec  RECORD;
BEGIN
    FOR rec IN SELECT * FROM test
    LOOP
          sqlstr := 'insert into test(c1, c2) values (' ||rec.c1||','
                                                                    ||'\''||rec.c2||'\')';
    RAISE NOTICE '%',sqlstr;
     execute sqlstr;
    END LOOP;
RETURN 'DONE';
END;

NOTICE: insert into test(c1, c2) values (1,'Hai1')
NOTICE: <NULL>

So i have created a null function.

sqlstr := 'insert into test(c1, c2) values (' ||ISNULL(rec.c1,'')||','
||'\''||rec.c2||'\')';

Now I got results as

NOTICE: insert into test(c1, c2) values (1,'Hai1')
NOTICE: insert into test(c1, c2) values (,'Hai2')
WARNING: Error occurred while executing PL/pgSQL function test_fn
WARNING: line 11 at execute statement

ERROR: parser: parse error at or near "," at character 34

The error is because of no value for column c1. If the column c1 is a string I might have replace it with empty string. I don't want to substitute with '0' which could work.

sqlstr := 'insert into test(c1, c2) values (' ||ISNULL(rec.c1,'0')||','
||'\''||rec.c2||'\')';

NOTICE: insert into test(c1, c2) values (1,'Hai1')
NOTICE: insert into test(c1, c2) values (0,'Hai2')

Total query runtime: 47 ms.
Data retrieval runtime: 0 ms.
1 rows retrieved.

How can I do that. Please advise me.

Thanks

Kumar

Re: How to avoid nulls while writing string for dynamic query

From

Tomasz Myrta

Date:

12 February 2004, 12:02:34

Dnia 2004-02-12 13:31, Użytkownik Kumar napisał:
> The error is because of no value for column c1. If the column c1 is a 
> string I might have replace it with empty string. I don't want to 
> substitute with '0' which could work.
>  
> sqlstr := 'insert into test(c1, c2) values (' ||ISNULL(rec.c1,'0')||','
>                                                                     
> ||'\''||rec.c2||'\')';

Substitute it with NULL value:
sqlstr := 'insert into test(c1, c2) values(' || coalesce(rec.c1,'NULL') 
||...

Regards,
Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

"Kumar"

Date:

13 February 2004, 03:54:05

I am having problem there. see what happens

sqlstr := 'insert into test(c1, c2) values ('||COALESCE(rec.c1,'NULL')||','       ||'\''||rec.c2||'\')';

WARNING:  Error occurred while executing PL/pgSQL function test_fn
WARNING:  line 8 at assignment
ERROR:  pg_atoi: error in "NULL": can't parse "NULL"

Dont forgot that c1 is int.

when i have like this
sqlstr := 'insert into test(c1, c2) values ('||COALESCE(rec.c1,NULL)||','       ||'\''||rec.c2||'\')';

NOTICE:  <NULL>
WARNING:  Error occurred while executing PL/pgSQL function test_fn
WARNING:  line 11 at execute statement
ERROR:  cannot EXECUTE NULL query

That is the problem i am facing. Please shed some light.

Thanks
Kumar

----- Original Message ----- 
From: "Tomasz Myrta" <jasiek@klaster.net>
To: "Kumar" <sgnerd@yahoo.com.sg>
Cc: "psql" <pgsql-sql@postgresql.org>
Sent: Thursday, February 12, 2004 6:13 PM
Subject: Re: [SQL] How to avoid nulls while writing string for dynamic query


> Dnia 2004-02-12 13:31, Użytkownik Kumar napisał:
> > The error is because of no value for column c1. If the column c1 is a
> > string I might have replace it with empty string. I don't want to
> > substitute with '0' which could work.
> >
> > sqlstr := 'insert into test(c1, c2) values (' ||ISNULL(rec.c1,'0')||','
> >
> > ||'\''||rec.c2||'\')';
>
> Substitute it with NULL value:
> sqlstr := 'insert into test(c1, c2) values(' || coalesce(rec.c1,'NULL')
> ||...
>
> Regards,
> Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

"Kumar"

Date:

13 February 2004, 04:41:30

Dear all,
I solved it using ISNULL function.
sqlstr := 'insert into test(c1, c2) values ('||ISNULL(rec.c1,'NULL')||','
>         ||'\''||rec.c2||'\')';
Thanks
kumar
----- Original Message ----- 
From: "Kumar" <sgnerd@yahoo.com.sg>
To: "Tomasz Myrta" <jasiek@klaster.net>
Cc: "psql" <pgsql-sql@postgresql.org>
Sent: Friday, February 13, 2004 10:23 AM
Subject: Re: [SQL] How to avoid nulls while writing string for dynamic query


> I am having problem there. see what happens
>
> sqlstr := 'insert into test(c1, c2) values
('||COALESCE(rec.c1,'NULL')||','
>         ||'\''||rec.c2||'\')';
>
> WARNING:  Error occurred while executing PL/pgSQL function test_fn
> WARNING:  line 8 at assignment
> ERROR:  pg_atoi: error in "NULL": can't parse "NULL"
>
> Dont forgot that c1 is int.
>
> when i have like this
> sqlstr := 'insert into test(c1, c2) values ('||COALESCE(rec.c1,NULL)||','
>         ||'\''||rec.c2||'\')';
>
> NOTICE:  <NULL>
> WARNING:  Error occurred while executing PL/pgSQL function test_fn
> WARNING:  line 11 at execute statement
> ERROR:  cannot EXECUTE NULL query
>
> That is the problem i am facing. Please shed some light.
>
> Thanks
> Kumar
>
> ----- Original Message ----- 
> From: "Tomasz Myrta" <jasiek@klaster.net>
> To: "Kumar" <sgnerd@yahoo.com.sg>
> Cc: "psql" <pgsql-sql@postgresql.org>
> Sent: Thursday, February 12, 2004 6:13 PM
> Subject: Re: [SQL] How to avoid nulls while writing string for dynamic
query
>
>
> > Dnia 2004-02-12 13:31, Użytkownik Kumar napisał:
> > > The error is because of no value for column c1. If the column c1 is a
> > > string I might have replace it with empty string. I don't want to
> > > substitute with '0' which could work.
> > >
> > > sqlstr := 'insert into test(c1, c2) values ('
||ISNULL(rec.c1,'0')||','
> > >
> > > ||'\''||rec.c2||'\')';
> >
> > Substitute it with NULL value:
> > sqlstr := 'insert into test(c1, c2) values(' || coalesce(rec.c1,'NULL')
> > ||...
> >
> > Regards,
> > Tomasz Myrta
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings

Re: How to avoid nulls while writing string for dynamic query

From

Tomasz Myrta

Date:

13 February 2004, 05:30:42

Dnia 2004-02-13 05:53, Użytkownik Kumar napisał:

> I am having problem there. see what happens
> 
> sqlstr := 'insert into test(c1, c2) values ('||COALESCE(rec.c1,'NULL')||','
>         ||'\''||rec.c2||'\')';

You are preparing a string, so make sure you have strings everywhere:
sqlstr := 'insert into test(c1, c2) values 
('||COALESCE(rec.c1::text,'NULL')||','||'\''||rec.c2||'\')';

Regards,
Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

"Kumar"

Date:

13 February 2004, 06:12:48

oh, ok understood.
What will happen for a timestamp field. Let us say c1 is a timestamp column.

sqlstr := 'insert into test(c1, c2) values
('||'\''||COALESCE(rec.c1,'NULL')||'\','
> >         ||'\''||rec.c2||'\')';

If this case the query will be
insert into test(c1,c2) values ('2004-02-13', 'Hai')

If there is a null value encountered i will return an error for the
following query
insert into test(c1,c2) values ('NULL', 'Hai')
ERROR:  Bad timestamp external representation 'NULL'

I think using 'CASE' this could be solved. But instead is there any other
simple way to do it.

Thanks a lot Mr. Tomasz Myrta
Kumar


----- Original Message ----- 
From: "Tomasz Myrta" <jasiek@klaster.net>
To: "Kumar" <sgnerd@yahoo.com.sg>
Cc: "psql" <pgsql-sql@postgresql.org>
Sent: Friday, February 13, 2004 12:03 PM
Subject: Re: [SQL] How to avoid nulls while writing string for dynamic query


> Dnia 2004-02-13 05:53, Użytkownik Kumar napisał:
>
> > I am having problem there. see what happens
> >
> > sqlstr := 'insert into test(c1, c2) values
('||COALESCE(rec.c1,'NULL')||','
> >         ||'\''||rec.c2||'\')';
>
> You are preparing a string, so make sure you have strings everywhere:
> sqlstr := 'insert into test(c1, c2) values
> ('||COALESCE(rec.c1::text,'NULL')||','||'\''||rec.c2||'\')';
>
> Regards,
> Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

Tomasz Myrta

Date:

13 February 2004, 07:04:28

Dnia 2004-02-13 08:13, Użytkownik Kumar napisał:
> oh, ok understood.
> What will happen for a timestamp field. Let us say c1 is a timestamp column.
> 
> sqlstr := 'insert into test(c1, c2) values
> ('||'\''||COALESCE(rec.c1,'NULL')||'\','
> 
>>>        ||'\''||rec.c2||'\')';
> 
> 
> If this case the query will be
> insert into test(c1,c2) values ('2004-02-13', 'Hai')
> 
> If there is a null value encountered i will return an error for the
> following query
> insert into test(c1,c2) values ('NULL', 'Hai')
> ERROR:  Bad timestamp external representation 'NULL'
It's because you can't use quotes with null. Valid query is:
insert into test(c1,c2) values (NULL, 'Hai');

Your dynamic query will then look like:

sqlstr := 'insert into test(c1, c2) values (' ||COALESCE('\'' || rec.c1 
|| '\'','NULL') ...

or more elegant:

sqlstr := 'insert into test(c1, c2) values (' 
||COALESCE(quote_literal(rec.c1),'NULL') ...

Regards,
Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

"Kumar"

Date:

13 February 2004, 08:13:48

Thanks Tomasz Myrta. It is wonderful. I am still amazed from where you guys
knowing the options like quote_literal, etc.

Kumar

----- Original Message ----- 
From: "Tomasz Myrta" <jasiek@klaster.net>
To: "Kumar" <sgnerd@yahoo.com.sg>
Cc: "psql" <pgsql-sql@postgresql.org>
Sent: Friday, February 13, 2004 1:37 PM
Subject: Re: [SQL] How to avoid nulls while writing string for dynamic query


> Dnia 2004-02-13 08:13, Użytkownik Kumar napisał:
> > oh, ok understood.
> > What will happen for a timestamp field. Let us say c1 is a timestamp
column.
> >
> > sqlstr := 'insert into test(c1, c2) values
> > ('||'\''||COALESCE(rec.c1,'NULL')||'\','
> >
> >>>        ||'\''||rec.c2||'\')';
> >
> >
> > If this case the query will be
> > insert into test(c1,c2) values ('2004-02-13', 'Hai')
> >
> > If there is a null value encountered i will return an error for the
> > following query
> > insert into test(c1,c2) values ('NULL', 'Hai')
> > ERROR:  Bad timestamp external representation 'NULL'
> It's because you can't use quotes with null. Valid query is:
> insert into test(c1,c2) values (NULL, 'Hai');
>
> Your dynamic query will then look like:
>
> sqlstr := 'insert into test(c1, c2) values (' ||COALESCE('\'' || rec.c1
> || '\'','NULL') ...
>
> or more elegant:
>
> sqlstr := 'insert into test(c1, c2) values ('
> ||COALESCE(quote_literal(rec.c1),'NULL') ...
>
> Regards,
> Tomasz Myrta

Re: How to avoid nulls while writing string for dynamic query

From

Tomasz Myrta

Date:

13 February 2004, 08:25:44

Dnia 2004-02-13 10:14, Użytkownik Kumar napisał:
> Thanks Tomasz Myrta. It is wonderful. I am still amazed from where you guys
> knowing the options like quote_literal, etc.
> 
> Kumar

Just read the manual ;-)
6.4. String Functions and Operators

Tomasz