When a DESCRIBE <table> or a SHOW COLUMNS IN <table> query is done, the
actual query is performed on tables in the information_schema
database. This might be what actually happens on the backend server but
this information is not really useful when we need to know which database
the query targets.
By passing the actual table names instead of the underlying table names,
the schemarouter is able to detect where these statements should be
routed.
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