These are important clauses in SELECT statements of DB2.
FETCH FIRST 1 ROW ONLY => Will limit the number of rows from the select statement. It avoids unnecessary I/O for select statements
OPTIMIZE FOR 2 ROWS => This is little different from previous one. The performance applies only for 2 rows. For the rest of the rows degradation of performance takes place.
Refer 238 SQL queries given in http://sqlnplsqlguru.blogspot.in
The QUERYNO clause specifies the number to be used for this SQL statement in EXPLAIN output and trace records.
How to override Isolation in select statement:
Isolation = > We can use WITH UR