知识点:在这里排在首位mysql可以用limit1,在其他数据库可以使用top 1 select continent,name from world x where x.name = ( select top 1 y.name from world y where x.continent=y.continent) 9.查找所有国家/地区的人口均≤25000000的大洲。然后查找与这些大洲相关的国家/地区的名称。显示姓名,大陆和人口。
1.题目:List each country name where the population is larger than that of 'Russia'. SELECTnameFROMworldWHEREpopulation>(SELECTpopulationFROMworldWHEREname='Russia'); 结果: 2.题目:Show the countries in Europe with a per capita GDP(gdp/population) greater than 'United Kingdom'. SELECT name FROM...
(SELECT continent FROM world WHERE name="Argentina" OR name="Australia") ORDER BY name ``` #Germany (population 80 million) has the largest population of the countries in Europe. Austria (population 8.5 million) has 11% of the population of Germany.Show the name and the population of each...
如果MySQL查询中使用了`WITH_MYSQLSELECTWITHIN`子句,但没有使用索引,可能有以下几种可能原因: 1. 索引不存在或没有被正确创建:确保表中有适当的索引,并且这些索引被正确创建。可以使用`SHOW INDEX FROM tableName`语句来检查索引的存在和状态。 2.查询条件不满足索引使用的前缀长度:一些类型的索引(如前缀索引)需要...
4. MySQL-过滤数据(WHERE语句)(642) 5. SQLZOO练习(一)SELECT BASICS,SELECT form world(546) 评论排行榜 1. SQLZOO练习二--SELECT from Nobel Tutorial(2) 2. SQLZOO练习(一)SELECT BASICS,SELECT form world(1) 推荐排行榜 1. HackerRank第一趴--Basic Select(1) 最新评论 1. Re:SQLZOO练习二...
我的标签 mysql(3) 随笔档案 2020年7月(3) 阅读排行榜 1. 【sql学习】经典面试50题-PostgreSQL语句练习(6033) 2. 【sql学习】sql数据分析实战——淘宝用户行为分析(965) 3. 【sql学习】——sqlzoo刷题(SELECT within SELECT Tutorial)(233) 推荐排行榜 1. 【sql学习】经典面试50题-PostgreSQL语句...
第4关SELECT within SELECT Tutorial - SQLZOO 练习select嵌套select,也就是子查询。 -- List each country name where the population is larger than that of 'Russia'.-- 练习where子查询, 从子查询里筛选数值。selectnamefromworldwherepopulation>(selectpopulationfromworldwherename='Russia')-- Show the coun...
这章我们主要讲解select操作。 select,即选择,其作用一般如下: 1.查询2.连接 首先我们来说说查询,下面有个题目: 表:Products+---+---+|ColumnName|Type|+---+---+|product_id|int||low_fats|enum||recyclable|enum|+---+---+product_id 是该表的主键(具有唯一值的列)。 low_fats 是枚举类型,取值...
sqlzoo练习答案--SELECTwithinSELECTTutorial This tutorial looks at how we can use SELECT statements within SELECT statements to perform more complex queries.name continent area population gdp Afghanistan Asia6522302550010020343000000 Albania Europe28748283174112960000000 Algeria Africa238174137100000188681000000 Andorra ...
IfORDER BYoccurs within a parenthesized query expression and also is applied in the outer query, the results are undefined and may change in a future version of MySQL. Use of column positions is deprecated because the syntax has been removed from the SQL standard. ...