You don't. You remove the 'Community=' and just use the columns you want to filter on:
...WHERE Department = 'CSE' AND Rank > 100
This will let the database engine know not to use Community as a filter column.
If you are trying to make one query that will handle both queries above, then maybe you could try using LIKE statement:
... WHERE Community LIKE '%' AND Department = 'CSE' AND Rank > 100
This would only be reliable is your Community values were made up of distinctive character combinations, so that when specifying a community you would only get that one community, rather than all that match the character combination.
[EDIT]
I may not be understanding your question, so please explain it better if this does not answer what you are trying to ask.
You cannot use any wildcard characters in equality filters, meaning you cannot have the pattern
ColumnName = '%'
, you can only use the wildcard characters with the
LIKE
construct for pattern matching when filtering results.
In order to include a particular column in the
WHERE
clause and not have it limit anything from your results, you need to use the pattern
ColumnName LIKE '%'
. This will match all entries in the column.