DB2 MQ functions

You can use the DB2® MQ functions to send messages to a message queue or to receive messages from the message queue. You can send a request to a message queue and receive a response.

The DB2 MQ functions support the following types of operations:

Send and forget, where no reply is needed.
Read or receive, where one or all messages are either read without removing them from the queue, or received and removed from the queue.
Request and response, where a sending application needs a response to a request.

The WebSphere® MQ server is located on the same IBM® i as DB2. The DB2 MQ functions are registered with DB2 and provide access to the WebSphere MQ server by using the MQI APIs.

The following table describes the DB2 MQ scalar functions.

Table 1. DB2 MQ Scalar Functions
Scalar function	Description
MQREAD	MQREAD returns a message in a VARCHAR variable from the MQ location specified by receive-service, using the policy defined in service-policy. This operation does not remove the message from the head of the queue but instead returns it. If no messages are available to be returned, a null value is returned.
MQREADCLOB	MQREADCLOB returns a message in a CLOB variable from the MQ location specified by receive-service, using the policy defined in service-policy. This operation does not remove the message from the head of the queue but instead returns it. If no messages are available to be returned, a null value is returned.
MQRECEIVE	MQRECEIVE returns a message in a VARCHAR variable from the MQ location specified by receive-service, using the policy defined in service-policy. This operation removes the message from the queue. If correlation-id is specified, the first message with a matching correlation identifier is returned; if correlation-id is not specified, the message at the beginning of queue is returned. If no messages are available to be returned, a null value is returned.
MQRECEIVECLOB	MQRECEIVECLOB returns a message in a CLOB variable from the MQ location specified by receive-service, using the policy defined in service-policy. This operation removes the message from the queue. If correlation-id is specified, the first message with a matching correlation identifier is returned; if correlation-id is not specified, the message at the head of queue is returned. If no messages are available to be returned, a null value is returned.
MQSEND	MQSEND sends the data in a VARCHAR or CLOB variable msg-data to the MQ location specified by send-service, using the policy defined in service-policy. An optional user-defined message correlation identifier can be specified by correlation-id. The return value is 1 if successful or 0 if not successful.
Notes: You can send or receive messages in VARCHAR variables or CLOB variables. The maximum length for a message in a VARCHAR variable is 32000. The maximum length for a message in a CLOB variable is 2 MB.

The following table describes the DB2 MQ table functions.

Table 2. DB2 MQ Table Functions
Table function	Description
MQREADALL	MQREADALL returns a table that contains the messages and message metadata in VARCHAR variables from the MQ location specified by receive-service, using the policy defined in service-policy. This operation does not remove the messages from the queue. If num-rows is specified, a maximum of num-rows messages is returned; if num-rows is not specified, all available messages are returned.
MQREADALLCLOB	MQREADALLCLOB returns a table that contains the messages and message metadata in CLOB variables from the MQ location specified by receive-service, using the policy defined in service-policy. This operation does not remove the messages from the queue. If num-rows is specified, a maximum of num-rows messages is returned; if num-rows is not specified, all available messages are returned.
MQRECEIVEALL	MQRECEIVEALL returns a table that contains the messages and message metadata in VARCHAR variables from the MQ location specified by receive-service, using the policy defined in service-policy. This operation removes the messages from the queue. If correlation-id is specified, only those messages with a matching correlation identifier are returned; if correlation-id is not specified, all available messages are returned. If num-rows is specified, a maximum of num-rows messages is returned; if num-rows is not specified, all available messages are returned.
MQRECEIVEALLCLOB	MQRECEIVEALLCLOB returns a table that contains the messages and message metadata in CLOB variables from the MQ location specified by receive-service, using the policy defined in service-policy. This operation removes the messages from the queue. If correlation-id is specified, only those messages with a matching correlation identifier are returned; if correlation-id is not specified, all available messages are returned. If num-rows is specified, a maximum of num-rows messages is returned; if num-rows is not specified, all available messages are returned.
Notes: You can send or receive messages in VARCHAR variables or CLOB variables. The maximum length for a message in a VARCHAR variable is 32000. The maximum length for a message in a CLOB variable is 2 MB. The first column of the result table of a DB2 MQ table function contains the message.