is no which indicates that the function cannot be executed in external servers therefore the function 902 d is marked as inexecutable in external databases next in step 707 the number of external databases that have so far occurred is calculated since the function contains only the column t 2 c 2 which already occurs the number of external databases remains set to 2 last the same evaluation is made for function 902 e in this case in step 708 it is determined whether the function 902 e contains functions marked as inexecutable in external databases since the function 902 d is already marked as inexecutable in external databases the function 902 e is also marked as inexecutable in external databases step 706 next in step 603 it is determined whether the number of databases contained in the query is one since the number of external databases is two an access procedure as shown in 1003 of fig1 is created step 605 for the query shown in 901 in the case where a database management system accesses a database of its own as shown in 1001 of fig1 creation is made of code 1001 b to scan table t 1 under condition length t 1 c 1 10 code 1001 c to scan table t 2 under condition length t 2 c 2 gt 15 and code 1001 a to couple execution results of the codes 1001 b and 1001 c under condition t 1 c 1 gt t 2.