Sql – Oracle extractValue Function not working

SELECT owner, table_name
  FROM dba_tables

This is assuming that you have access to the DBA_TABLES data dictionary view. If you do not have those privileges but need them, you can request that the DBA explicitly grants you privileges on that table, or, that the DBA grants you the SELECT ANY DICTIONARY privilege or the SELECT_CATALOG_ROLE role (either of which would allow you to query any data dictionary table). Of course, you may want to exclude certain schemas like SYS and SYSTEM which have large numbers of Oracle tables that you probably don't care about.

Alternatively, if you do not have access to DBA_TABLES, you can see all the tables that your account has access to through the ALL_TABLES view:

SELECT owner, table_name
  FROM all_tables

Although, that may be a subset of the tables available in the database (ALL_TABLES shows you the information for all the tables that your user has been granted access to).

If you are only concerned with the tables that you own, not those that you have access to, you could use USER_TABLES:

SELECT table_name
  FROM user_tables

Since USER_TABLES only has information about the tables that you own, it does not have an OWNER column – the owner, by definition, is you.

Oracle also has a number of legacy data dictionary views-- TAB, DICT, TABS, and CAT for example-- that could be used. In general, I would not suggest using these legacy views unless you absolutely need to backport your scripts to Oracle 6. Oracle has not changed these views in a long time so they often have problems with newer types of objects. For example, the TAB and CAT views both show information about tables that are in the user's recycle bin while the [DBA|ALL|USER]_TABLES views all filter those out. CAT also shows information about materialized view logs with a TABLE_TYPE of "TABLE" which is unlikely to be what you really want. DICT combines tables and synonyms and doesn't tell you who owns the object.

Try this, either your case should return number or varchar, right now your case return '0' as varchar and else as number. Either both should return a varchar or both should return a number.

When Both return varchar

CASE WHEN d.cancelled = 'TRUE' 
     THEN '0' 
     ELSE to_char((to_char(b.owed)) - (to_char(d.paid)))
     END AS balance,

OR

When Both return number

CASE WHEN d.cancelled = 'TRUE' 
         THEN 0 
         ELSE (to_char(b.owed)) - (to_char(d.paid))
         END AS balance,

OR

When Both return number

CASE WHEN d.cancelled = 'TRUE' 
         THEN 0 
         ELSE (b.owed - d.paid)
         END AS balance,