Bad performance with Pervasive SQL 2000.i ??

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I created a small database with 5 tables in Pervasive SQL.2000i (max.record number: 300). I wrote a simple SQL statement in SQL Data Manager direct in PCC. I received very fast the result (1 sec). Then I added a sub-select in WHERE condition of SQL statement. The query runs 50 sec. For a comparsion I migrated the Pervasive Db into MS SQL Server 7 Db (same tables, same data). I received the query after 1 sec (!!!). It was the same SQL statement with a sub-select. What is wrong ? Why needs Pervasive ODBC so long ? It would be nice to have a little idea ! Thanks.