MQREAD scalar function

The MQREAD function returns a message from a specified IBM® MQ location without removing the message from the queue.

The schema is DB2MQ.

The MQREAD function returns a message from the IBM MQ location that is specified by receive-service, using the quality-of-service policy that is defined in service-policy. Performing this operation does not remove the message from the queue that is associated with receive-service, but instead returns the message at the beginning of the queue.

receive-service: An expression that returns a value that is a built-in character string or graphic string data type that is not a LOB. The value of the expression must not be an empty string or a string with trailing blanks. The expression must have an actual length that is no greater than 48 bytes. The value of the expression must refer to a service point that is defined in the DB2MQ.MQSERVICE table. A service point is a logical end-point from which a message is sent or received. A service point definition includes the name of the IBM MQ queue manager and the name of the queue. See IBM MQ Application Messaging Interface for more details.
If receive-service is not specified or is the null value, DB2.DEFAULT.POLICY is used.
service-policy: An expression that returns a value that is a built-in character string or graphic string data type that is not a LOB. The value of the expression must not be an empty string or a string with trailing blanks. The expression must have an actual length that is no greater than 48 bytes. The value of the expression must refer to a service policy that is defined in the DB2MQ.MQPOLICY table. A service policy specifies a set of quality-of-service options that are to be applied to this messaging operation. These options include message priority and message persistence. See IBM MQ Application Messaging Interface for more details.
If service-policy is not specified or is the null value, DB2.DEFAULT.POLICY is used.

The result of the function is a varying-length string with a length attribute of 4000. The result can be null. If no messages are available to be returned, the result is the null value.

The CCSID of the result is the system CCSID that was in effect at the time that the IBM MQ function was installed into Db2.

Examples

Example 1: Retrieve the message at the beginning of the queue that is specified by the default service (Db2.DEFAULT.SERVICE), using the default policy (Db2.DEFAULT.POLICY)

   SELECT MQREAD()
     FROM SYSIBM.SYSDUMMY1;

The message at the beginning of the queue specified by the default server and using the default policy is returned as VARCHAR(4000).

Example 2: Read the message from the beginning of the queue specified by the service MYSERVICE, using the default policy (Db2.DEFAULT.POLICY)

   SELECT MQREAD('MYSERVICE')
     FROM SYSIBM.SYSDUMMY1;

The message at the beginning of the queue specified by MYSERVICE and using Db2.DEFAULT.POLICY is returned as VARCHAR(4000).

Example 3: Read the message from the beginning of the queue specified by the service MYSERVICE, using the policy MYPOLICY

   SELECT MQREAD('MYSERVICE','MYPOLICY')
     FROM SYSIBM.SYSDUMMY1;

The message at the beginning of the queue specified by MYSERVICE and using the policy MYPOLICY is returned as VARCHAR(4000).