DB2 TIPS

Select unknown values only

For performance reasons it is better to select as few columns as possible. The optimizer may choose techniques like Index-only access. Besides it makes the query easier to read and maintain. In the following query selects five columns of table FOTB100. The first two columns are also used in the where-clause with “=”-predicates. So the values of these columns are no surprise and therefore it is not necessary to select these columns. So leave them out of the column-list.  SELECT         REK_NR       , PE_TX_REF       , ST_TS       , ST       , PRI  INTO        :REK-NR          OF FINTXSTH      , :PE-TX-REF     OF FINTXSTH      , :ST-TS              OF FINTXSTH      , :ST                   OF FINTXSTH      , :PRI                  OF FINTXSTH FROM  FOTB100  WHERE  REK_NR     = :REK-NR    OF FINTXST    AND  PE_TX_REF  = :PE-TX-REF OF FINTXST