问题 单项选择题

下面关于为基本表建立索引的说法正确的是______。

A.表的候选码

B.在where查询子旬中引用率较低的属性

C.未参与连接操作的属性

D.在order by子句中出现的属性

答案

参考答案:D

解析: 对于基本表,下面一些属性上可考虑建立索引: ①表的主码。一般由DBMS自动建立索引。 ②在where查询子句中引用率较高的属性。 ③参与了连接操作的属性。 ④在order by子句、group by子句中出现的属性。 ⑤在某一范围内频繁搜索的属性和按照排序顺序频繁检索的属性。 ⑥在where子句中包含的一个关系的多个属性,可以考虑在这些属性上建立多属性索引。

完形填空
完形填空 (共15小题,每小题1分,满分15分)
All over the world people swim for fun. Swimming is enjoyed by people of 1Ages, from the very young to the very old. There are many places for people to swim in swimming pools. Many schools, hotels and clubs have swimming pools. Some people have pools of   2  in their yards.
Swimming is one of 3 forms of exercise. It can   4 hearts and bodies strong. It can also help blood circulate (循环). Handicapped people can keep their bodies in better condition by swimming  5 they can’t enjoy sports.
 6  is a good idea for parents to see to it (务必做到) that their children learn to swim  7  an early age. So their children will 8  it for the rest of their lives.
There are many rules for water safety. These rules can help save not only your life   9  the life of a friend. First of all, know 10  . Many schools   11  swimming lessons to children. Adults (成人) can learn to swim at public pools.   12   rule to remember is never to swim   13  . Always swim with a friend and know   14   in the water at all times. It is best to swim   15  in safe places if you are beginners. If everyone learned to swim and obeyed the rules for water safety, most drawing (溺水) could be avoided.
小题1:
A.allB.anyC.someD.both
小题2:
A.themselvesB.their ownC.theirs ownD.their own’s
小题3:
A.goodB.betterC.bestD.the best
小题4:
A.helpB.letC.makeD.show
小题5:
A.thoughB.as C.soD.until
小题6:
A.ThatB.ThereC.ThisD.It
小题7:
A.overB.during C.atD.on
小题8:
A.learnB.enjoyC.stopD.know
小题9:
A.and aimB.stillC.and yet D.but also
小题10:
A.how to swimB.why swimmingC.how swimmingD.why to swim
小题11:
A.haveB.takeC.giveD.make
小题12:
A.The other oneB.OtherC.An otherD.Another
小题13:
A.aloneB.yourselfC.lonelyD.together
小题14:
A.who that person isB.where that person is
C.who is that personD.where is that person
小题15:
A.nearlyB.hardlyC.almostD.only
单项选择题