I have a table contain 1000 record, I would like to search whether got any record got the same data, for example I would like to check 'tel_no' field, see whether the record contain 2 or more same data inside, anybody knows how to write an sql statement to get it out?
Name tel_no address sex
a 5555 abc m
b 5656 bbb f
c 5555 dfdf m
how to write a sql statement to see find out the field 'tel_no' actually contain same data '5555' twice here?