1.問題：Query a list of?CITY?names from?STATION?with even?ID?numbers only. You may print the results in any order, but must exclude duplicates from your answer.

答案：SELECT DISTINCT city FROM station WHERE MOD(id,2)=0;

解析：要輸出偶數(shù)id的城市名稱且不能出現(xiàn)重復(fù)，distinct是去重，mod求余函數(shù)

2.Let N?be the number of?CITY?entries in?STATION, and let N`?be the number of distinct?CITY?names in?STATION; query the value of? N-N`?from?STATION. In other words, find the difference between the total number of?CITY?entries in the table and the number of distinct?CITY?entries in the table.

答案：SELECT COUNT(city)-COUNT(DISTINCT city) FROM station;

解析：通過統(tǒng)計(jì)函數(shù)進(jìn)行數(shù)據(jù)統(tǒng)計(jì)并進(jìn)行運(yùn)算。

3.Query the two cities in?STATION?with the shortest and longest?CITY?names, as well as their respective lengths (i.e.: number of characters in the name). If there is more than one smallest or largest city, choose the one that comes first when ordered alphabetically.

答案：

SELECT CITY, LENGTH(CITY)
FROM STATION ORDER BY LENGTH(CITY),CITY LIMIT 1;
SELECT CITY, LENGTH(CITY)
FROM STATION ORDER BY LENGTH(CITY) DESC,CITY LIMIT 1;

解析：首先查詢城市名字，城市長(zhǎng)度通過長(zhǎng)度排序，升序排序找到最短名字，使用limit來(lái)返回第一行數(shù)據(jù)；

4.Query the list of?CITY?names starting with vowels (i.e.,?a,?e,?i,?o, or?u) from?STATION. Your result?cannot?contain duplicates.

答案：

SELECT DISTINCT CITY
FROM STATION
WHERE LOWER(SUBSTR(CITY,1,1)) in('a','e','i','o','u') ;

解析：因?yàn)槭欠秶x擇所以選擇in，不能重復(fù)用distinct，截取城市名字的第一個(gè)字母并轉(zhuǎn)成小寫。

5.Query the list of?CITY?names ending with vowels (a, e, i, o, u) from?STATION. Your result?cannot?contain duplicates.

答案：

SELECT DISTINCT CITY FROM STATION
WHERE CITY REGEXP '[aeiou]$';

解析：regexp是mysql中的正則表達(dá)式，表示匹配到aeiou就提出來(lái)，其中有幾個(gè)定位符：“.”代表任意字符；在中括號(hào)外：“^”代表文本開始；“$”文本結(jié)束

查詢首字母及最后一個(gè)字母為（aeiou）時(shí)將其變成^[aeiou].*[aeiou]$

查詢除了這些字母外，其他作為首字母的城市名字變成^[^aeiou]：中括號(hào)內(nèi)的^表示除了這些之外

6.Query the list of?CITY?names from?STATION?that?do not end?with vowels. Your result cannot contain duplicates.

答案：select distinct city from station where city not regexp '[aeiou]$';

分析：用not將最后為元音的都排除掉。

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轉(zhuǎn)載于:https://www.cnblogs.com/gnn0426/p/9672274.html

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