sql delete from with relation
# your select statement acctually works (and I don't know wich is your statement...).
# You must replace only
SELECT ...
# with
DELETE [table name or alias]
# and leave everything else the same.
# e.g:
DELETE cu FROM CustomUser cu
left join RoleMapping on cu.id = RoleMapping.principalId
WHERE RoleMapping.roleId = 1;