SQL语言中,条件表示年龄在40至50之间的表达式为 ( )。
A. IN (40,50)
BETWEEN 40 AND 50
C. BETWEEN 40 OR 50
D. BETWEEN 40 ,50
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拼接2个以上select语句查询结果集,用以下( )个语句。
A. order by
B. union
C. join
D. from
排序用下面( )个子句。
A. group by
B. order by
C. ASC
D. where
求平均值用( )个聚合函数。
A. avg( )
B. max( )
C. average( )
D. mean( )
分组查询的关键字是( )
A. order by
B. from
C. group by
D. group