SQL string match numbers, varying length

[kenbanana]

I am looking up which exchange services which telephone numbers, from a table of fragmentary numbers that show which exchange services them. So my table contains, for example:\[code\]id |exchcode |exchname |easting|northin|leadin |-----------------------------------------------------------------12122 |SNL/UC |SANDAL |43430 |41306 |1924240 |12123 |SNL/UC |SANDAL |43430 |41306 |1924241 |881 |SNL/UD |SANDAL |43430 |41306 |1924249 |2456 |BD/BCC/1 |BRADFORD CABLE |41627 |43262 |192421 |4313 |NEY/UB |NORMANTON |43847 |42289 |192422 |12124 |SNL/UC |SANDAL |43430 |41306 |192425 |9949 |OBE/UB |HORBURY OSSETT |42857 |41971 |192428 |9987 |OBE/UB |WAKEFIELD |42857 |41971 |1924 |\[/code\](sorry, formatting a bit rubbish)leadin is the leading part of the phone number I have to match (stored as a VARCHAR, not a number)And I am supplied with a phone number 1924283777 (not real)how do I query to get the best match from the above table (It should pick exchange id 9949), or do I deal with it in code after I've done the query (php)tl;dr: variable length for values of leadin column, want best match with a number longer than leadin.