Table not returning correct information

Question

We had a problem where doing a select count(*) returned a number, but then when a select * was issued not rows were returned. Many iterations were tried. Some returning rows and others not. Then when trying to truncate FK errors occurred. Does anyone know what might have been the problem? Our solution was to drop and re-create the tables. This was in a test environment, but we don't want this to happen in production.
Thanks.

Answer 1

Something doesn't sound right to me. I haven't seen this happen in our Oracle databases but have seen this happen with a DB2 database
when an index was corrupt. The solution was to rebuild the index in that case. I'd issue a statement to validate the structure of the table
and its indexes:
analyze table table_name validate structure cascade;
From the 8.1.7 SQL manual:
VALIDATE STRUCTURE
Specify VALIDATE STRUCTURE to validate the structure of the analyzed object. The statistics collected by this clause are not used by the Oracle optimizer, as are
statistics collected by the COMPUTE STATISTICS and ESTIMATE STATISTICS clauses.
For a table, Oracle verifies the integrity of each of the table's data blocks and rows.
For a cluster, Oracle automatically validates the structure of the cluster's tables.
For a partitioned table, Oracle also verifies that each row belongs to the correct partition. If a row does not collate correctly, its rowid is inserted into the
INVALID_ROWS table.
For a temporary table, Oracle validates the structure of the table and its indexes during the current session.
For an index, Oracle verifies the integrity of each data block in the index and checks for block corruption. This clause does not confirm that each row in the table
has an index entry or that each index entry points to a row in the table. You can perform these operations by validating the structure of the table with the
CASCADE clause (described below).
Oracle stores statistics about the index in the data dictionary views INDEX_STATS and INDEX_HISTOGRAM.
See Also: Oracle8i Reference for information on these views
Validating the structure of an object prevents SELECT, INSERT, UPDATE, and DELETE statements from concurrently accessing the object. Therefore, do not use this
clause on the tables, clusters, and indexes of your production applications during periods of high database activity.
If Oracle encounters corruption in the structure of the object, an error message is returned to you. In this case, drop and re-create the object.
INTO table
Specify a table into which Oracle lists the rowids of the partitions whose rows do not collate correctly. If you omit schema, Oracle assumes the list is in
your own schema. If you omit this clause altogether, Oracle assumes that the table is named INVALID_ROWS. The SQL script used to create this table
is UTLVALID.SQL.
CASCADE
Specify CASCADE if you want Oracle to validate the structure of the indexes associated with the table or cluster. If you use this clause when validating a
table, Oracle also validates the table's indexes. If you use this clause when validating a cluster, Oracle also validates all the clustered tables' indexes,
including the cluster index.
If you use this clause to validate an enabled (but previously disabled) function-based index, validation errors may result. In this case, you must rebuild the
index.