Placing each stack trace line in a new row in string form (without explicit columns for the class, file and line number) is a little silly. Instead of aggregating the stack trace into a single line, a separate column for the various exception fields would have been better because it would allow searches based on exception classes/messages or stack traces.

IMO, the nicest approach table structure would be akin to:

CREATE TABLE logging_event_exception (
event_id INT NOT NULL,
i SMALLINT NOT NULL, – 0 for the topmost exception, incremented by one for each nested exception
exception_class VARCHAR(256) NOT NULL,
exception_msg VARCHAR(1024),
stack_trace VARCHAR(16384)
PRIMARY KEY(event_id, i),
FOREIGN KEY (event_id) REFERENCES logging_event(event_id));

where i would be incremented by one for each 'root cause'. If in addition, the LOGGING_EVENT table contained the total number of nested exception, it would be rather easy to retrieve the original exception plus its root causes.