سوال: انتخاب چند رکورد از هر گروه

این جدول 45 سطر دارد

name ______ id_country _______ id_city ____ id

add_1 _________ 1 _______==_____ 1 ______ 1
add_2 _________ 1 _______________ 1 ______ 2
add_3 _________ 1 _______________ 1 ______ 3
add_4 _________ 1 _______________ 1 ______ 4
add_5 _________ 1 _______________ 1 ______ 5
add_6 _________ 2 _______==_____ 1 ______ 6
add_7 _________ 2 _______________ 1 ______ 7
add_8 _________ 2 _______________ 1 ______ 8
add_9 _________ 2 _______________ 1 ______ 9
add_10 _________ 2 _______________ 1 _____ 10
add_11 _________ 3 _______==_____1 ______ 11
add_12 _________ 3 ______________ 1 ______ 12
add_13 _________ 3 ______________ 1 ______ 13
add_14 _________ 3 ______________ 1 ______ 14
add_15 _________ 3 ______________ 1 ______ 15

add_16 _________ 1 _______________ 2 ______ 16
add_20 _________ 1 _______________ 2 ______ 20

add_21 _________ 1 _______________ 3 ______ 21
add_30 _________ 1 _______________ 3 ______ 25

add_26 _________ 2 _______________ 2 ______ 26
add_30 _________ 2 _______________ 2 ______ 30

add_31 _________ 2 _______________ 3 ______ 31
add_35 _________ 2 _______________ 3 ______ 35

add_36 _________ 3 _______________ 2 ______ 36
add_40 _________ 3 _______________ 2 ______ 40

add_41 _________ 3 _______________ 3 ______ 41
add_45 _________ 3 _______________ 3 ______ 45

- - , .