The maximum number of USING variables you can specify in a USING request modifier is 2,536.
Each USING variable name must be unique in a USING request modifier.
The USING variable construct (:using_variable_name) is valid anywhere a character, numeric, or byte constant is valid. The constant values in the client system data record must match, item for item, the USING description of those values. Also, the constants in the data record must appear in the order in which they are defined in the USING clause.
You cannot use a USING variable to specify a column position in a GROUP BY or ORDER BY clause.
One USING clause can only modify one request. If several requests require USING variables, each request must be associated with its own USING row identifier.