это будет работать:
SELECT concat(SUBSTRING("1234587920", 1, 2),"-",SUBSTRING("1234587920",3,2),"-
",SUBSTRING("1234587920", 5, 2),"-",
SUBSTRING("1234587920", 7, 2),"-",
SUBSTRING("1234587920", 9, 2)) AS ExtractString;
для вашего запроса к таблице:
SELECT concat(SUBSTRING(mobile_number, 1, 2),"-
",SUBSTRING(mobile_number,3,2),"-",SUBSTRING(mobile_number, 5, 2),"-",
SUBSTRING(mobile_number, 7, 2),"-",
SUBSTRING(mobile_number, 9, 2)) ExtractString from tablename;