Updating an empty character column

Hi,

I have a question regarding the default value pf a CHAR(1) column.

My apologies if this is really obvious. I was just not able to find
an appropriate answer in my searches.

I have a table with a CHAR(1) field in it. This has already
some data in it. I simply need to set the CHAR(1) field to 'N'
whenever it is null.

I altered the table so It will have a
default value for the column. So, any data entered from now on
should be fine. However, the data alterady present in the data
needs to be modified as well.

Here are the sample statements:

SQL> create table test ( a int, b char(1));

Table created.

SQL> insert into test (a) values (9);

1 row created.

SQL> insert into test (a) values (99);

1 row created.

SQL> alter table test modify b default 'N';

Table altered.

SQL> insert into test (a) values (999);

1 row created.

SQL> insert into test (a) values (9999);

1 row created.

SQL> select * from test;

A B
---------- -
9
99
999 N
9999 N

SQL> update test set b='N' where b!='N';

0 rows updated.

SQL> update test set b='N' where b='';

0 rows updated.

SQL> update test set b='N' where b=' ';

0 rows updated.

SQL> update test set b='N' where b=NULL;

0 rows updated.

SQL> update test set b='N' where b='NULL';

0 rows updated.

The following seems to work.

SQL> update test set b='N' where a=9;

1 row updated.

SQL> update test set b='N' where a=99;

1 row updated.

SQL> select * from test;

A B
---------- -
9 N
99 N
999 N
9999 N

However, I cannot afford to the same with my real data
as there are many rows and the value of column A is not unique. In other
words, I could have records with values as follows:

9 A
9 N
9 U

So, I cannot afford to update all columns where A=9 and set them to N.
Any suggestions would be greatly appreciated.

Thank you,
Sankar.

Ah hah ... what you want is the predicate:

Code:

where b Is Null

the opposite of which is

Code:

where b Is Not null

Quote:

Originally Posted by slimdave

Ah hah ... what you want is the predicate:

Code:

where b Is Null

the opposite of which is

Code:

where b Is Not null

I know you know the answer, but just to be painfully obvious I created a small demonstration of the
difference between NULL and 'NULL'. Parden my overzealousness. ;)

Code:

1 SELECT '|' || ASCII(NULL) || '| != ' || 2 ASCII('N') || ' + ' || 3 ASCII('U') || ' + ' || 4 ASCII('L') || ' + ' || 5 ASCII('L') "NULL != 'NULL'" 6* FROM dual SQL> / NULL != 'NULL' ----------------------- || != 78 + 85 + 76 + 76

Thank you very much slimdave and galdolf989 for the solutions. It worked like a charm. Truly appreciate your quick and detailed responses.