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MySQL Internals Manual OUT Parameter Set

Starting with MySQL 5.5.3, prepared statements can bind OUT parameters of stored procedures. They are returned as an extra resultset in the multi-resultset response. The client announces it can handle OUT parameters by settting the CLIENT_PS_MULTI_RESULTS capability.

To distinguish a normal resultset from an OUT parameter set, the EOF_Packet or (if the CLIENT_DEPRECATE_EOF capability flag is set) OK_Packet that follows its field definition has the SERVER_PS_OUT_PARAMS flag set.


The closing EOF_Packet does NOT have neither the SERVER_PS_OUT_PARAMS flag nor the SERVER_MORE_RESULTS_EXISTS flag set. Only the first EOF_Packet has.