问题
单项选择题
关系数据库的任何检索操作所涉及的3种基本运算不包括( )。
A．连接
B．比较
C．选择
D．投影
答案
参考答案：B
解析： 关系数据库中检索操作涉及的3种关系运算包括选择、投影和连接；选项B)中的比较不属于关系运算。
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关系数据库的任何检索操作所涉及的3种基本运算不包括( )。
A．连接
B．比较
C．选择
D．投影
参考答案：B
解析： 关系数据库中检索操作涉及的3种关系运算包括选择、投影和连接；选项B)中的比较不属于关系运算。
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| My mother used to ask me what the most important part of the body was. Through the years I would take a 1 at what I thought was the correct answer. When I was younger, I thought 2 was very important to us as humans, so I said, "My ears, Mommy." She said, "No. Many people are 3 . Keep thinking about it and I will ask you again soon." Several years passed before she asked me again. Since making my first 4 , I had often thought over the question. So this time I told her, "Mommy, sight is very important to everybody, so it must be our eyes." She looked at me and told me, "You are 5 fast, but the answer is not correct because there are many people who are blind." 6 the years, Mother asked me a couple more 7 and always her answer was, "No, but you are getting 8 every year, my child." Last year, my Grandpa 9 . Everybody was heart-broken. Everybody was crying. My Mom looked at me when it was our 10 to say our final good-bye to Grandpa. She asked me, "Do you know the most important body part yet, my dear?" I was 11 when she asked me this now. I always thought this was a 12 between her and me. She saw the 13 on my face and told me, "The question is very important. It shows that you have really 14 your life." I saw her eyes wet up with tears. She said, "My dear, the most important body part is your 15 ." I asked, "Is it because they hold up your head?" She replied, "No, it is 16 on them a crying friend or loved one can rest their heads. I only hope that you have enough 17 and friends that you will have a shoulder to cry 18 when you need it." Then and there I knew the most important body part is not a 19 one. It is sympathetic to the pain of 20 . | ||||
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