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Why not download the English Wikipedia? There are compressed SQL files of various sizes, and it should certainly be large enough for you
The main articles are XML, so inserting them into the db is a bit more of a problem, but you might find there are other files there that suit you. For example, the inter-page links SQL file is 2.3GB compressed. Have a look at https://en.wikipedia.org/wiki/Wikipedia:Database_download for more info.
Oskar
This is what I am using for learning sql: employees-db
this is a sample database with an integrated test suite, used to test your applications and database servers
According to launchpad.net the database has moved to github.
The database contains about 300,000 employee records with 2.8 million salary entries. The export data is 167 MB, which is not huge, but heavy enough to be non-trivial for testing.
The data was generated, and as such there are inconsistencies and subtle problems. Rather than removing them, we decided to leave the contents untouched, and use these issues as data cleaning exercises.