How does the value of the system variable max_allowed_packet affect the results of string-valued functions?

The string-valued function returns NULL if the length of the result is greater than the value of the max_allowed_packet system variable. Actually, max_allowed_packet is a dynamic global variable that can accept integer type values. These values ​​can only be set for sessions. It accepts a minimum value of 1024 and a maximum value of 1073741824. The default value of this system variable is 1048576.

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