Will something like this work for you??
index=abc sourcetype=xyz error earliest=-24h@h latest=now| rex field=_raw "\] - (?[^|]+).*"| stats count by CompleteErrorString | appendpipe [stats sum(count) as count | eval CompleteErrorString="Total Count of different error strings"]
Output
CompleteErrorString count
Client is not configured properly in the database 22
Client is not having enough permission to access the application 7
SOAP Fault occurred 14
Total Count of different error strings 43
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