9. Which statement is true regarding the INTERSECT operator?
对交集操作那个说法正确？
A. It ignores NULL values.
B. Reversing the order of the intersected tables alters the result.
C. The names of columns in all SELECT statements must be identical.
D. The number of columns and data types must be identical for all SELECT statements in the query.对于所有SELECT查询语句，列的数量和数据类型必须相同。
Answer: D