考察limit offset,ifnull, 记得distinct
① selete * from testtable limit 2,1;
② selete * from testtable limit 2 offset 1;
注意:
1.数据库数据计算是从0开始的
2.offset X是跳过X个数据,limit Y是选取Y个数据
3.limit X,Y 中X表示跳过X个数据,读取Y个数据
这两个都是能完成需要,但是他们之间是有区别的:
①是从数据库中第三条开始查询,取一条数据,即第三条数据读取,一二条跳过
②是从数据库中的第二条数据开始查询两条数据,即第二条和第三条
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Write a SQL query to get the second highest salary from the Employee
table.
+----+--------+ | Id | Salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+
For example, given the above Employee table, the query should return 200
as the second highest salary. If there is no second highest salary, then the query should return null
.
+---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+
select ifnull(select distinct Salary
from Employee
order by Salary
limit 1 offset 1, null)
as HighestSecondSalary