The present disclosure relates to a computer system for inserting multiple data items in a relation, the relation being stored on a server computer of the computer system, the relation comprising data items, wherein the data items are encrypted with a first encryption method in the relation, wherein the data items form a partially ordered set in the relation, the partial order being formed with respect to the data items in non-encrypted form. The computer system further comprises a client system, wherein for inserting multiple encrypted data items in the partially ordered set: the client system is configured for determining that the multiple data items have a same insert position in the partially ordered set; sorting the multiple encrypted data items in accordance with a linear order corresponding to the order in which the encrypted data items are stored in the relation with respect to the partial ordered set, wherein depending on the insert position the sorting is performed in ascending or descending order; encrypting the multiple data items using the first encryption method; and the server system is configured for inserting the encrypted data items in the partially ordered set consecutively in their sorted order.