多项选择题

A. The tables being joined have NOT NULL columns.B. The……

In which two cases would you use an outer join? （）

A. The tables being joined have NOT NULL columns.
B. The tables being joined have only matched data.
C. The columns being joined have NULL values.
D. The tables being joined have only unmatched data.
E. The tables being joined have both matched and unmatched data.
F. Only when the tables have a primary key/foreign key relationship.

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