the "tables" inside DICTIONARY dont exist as SAS datasets anywhere. they are "created" in real time as you reference them. presenting the information in a tabular format is useful for many reasons, and many database systems have these "schema information tables". so for example, when you query DICTIONARY.LIBNAMES, the SQL software asks the SAS supervisor for a list of libnames defined "at this moment", and packages up the answer as if it really were a table. thats why using a where clause can be important. select * from DICTIONARY.COLUMNS; means opening every dataset, in every visible libname, to inspect its column names - these are not stored centrally with SAS, they are stored distributed in each dataset. WHERE libname = 'FRED' allows us to skip all the other libraries
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