Which of the following SQL statements will return the year and average salary for all employees hired within a given year that have a salary greater than $30,000?()
题目内容(请给出正确答案)
Which of the following SQL statements will return the year and average salary for all employees hired within a given year that have a salary greater than $30,000?()
A.SELECT * FROM t1 UNION SELECT * FROM t2
B.SELECT * FROM t1 UNION DISTINCT SELECT * FROM t2
C.SELECT * FROM t1 INTERSECT SELECT * FROM t2
D.SELECT * FROM t1 WHERE (c1,c2)= (SELECT c1,c2 FROM t2)
