>"where name like 'Ab%'" returns any entry of the table, where name start with "Ab" except those ones containing character "-". Using "starting with" or "containing"
>the same database entries are missing.

Firebird simply doesn't exclude entries depending on which character follows what you're searching for. It might be like Helen said (different case) or maybe it can be something like a damaged index. Fb 2.5.1 has a problem with multifield indexes that can contain <null>, and I wouldn't surprise me if this could lead to apparently missing records (although I haven't heard or experienced this, just that GROUP BY can return duplicates). If you are using Fb 2.5.1 or the database has been in Fb 2.5.1 and you haven't restored the database since, then either upgrade to a newer version (and backup/restore your database) or try avoiding multi-field indexes.

If this isn't the case, Rainer, then please provide us with a more detailed description of your problem, including DDL of the table, your SQL statement, chosen PLAN and a few examples of records that should be returned including some that aren't. Also, it might be helpful if you include which Firebird version, character set and collation you are using. Many of us would be greatly surprised (an understatement) if you could provide a reproducible test case demonstrating such a severe Firebird error.

HTH,
Set