I have used the NVL function in several other posts but here is another example. First a table is created. It has never been analyzed so its last_analyzed date is null. The NVL function spots this and replaces the null by the text, Not yet:
SQL> create table andrew (col1 number)
2 /
Table created.
SQL> select nvl(to_char(last_analyzed),'Not yet')
2 from dba_tables
3 where table_name = 'ANDREW'
4 /
NVL(TO_CH
---------
Not yet
SQL>
If you don't like the NVL function, you can use the SQL*Plus SET NULL statement instead. Here is one way to use it:
SQL> set null 'Null'
SQL> select last_analyzed from dba_tables
2 where table_name = 'ANDREW'
3 /
LAST_ANAL
---------
Null
SQL>
And here is another:
SQL> col last_analyzed null Never
SQL> select last_analyzed from dba_tables
2 where table_name = 'ANDREW'
3 /
LAST_ANAL
---------
Never
SQL>
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