Qlik could connect to the database (either with standard odbc/oledb or any custom driver) which host your datawarehouse and then you could pull all tables with all fields and all records - one after another and/or you used any queries which pull certain data from any tables. For everything you will need to use sql-statements like you would apply directly in the database.
Most often it's not very sensible to pull all data and it's quite likely that it needs multiple adjustments (renaming from fields and de-normalizing the data - not everything is a must but it's recommended to consider it) to create an useful datamodel in Qlik.
Therefore, yes it's possible to get all needed data from the datawarehouse but it might not so easy as you hoped for.
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