标签：you 行数据 res sts 函数 return div date weather
解法1：
CASE ... WHEN ..
ELSE END;
# Write your MySQL query statement below
UPDATE salary
SET
sex = CASE sex
WHEN "m" THEN "f"
ELSE "m"
END;
解法2：
使用MySQL的if函数，类似于java的三目运算， if(sex = ‘m‘,‘f‘,‘m‘)，如果sex 为m，则返回f，如果为f，返回m。
update salary set sex = if(sex = ‘m‘,‘f‘,‘m‘)
# Write your MySQL query statement below UPDATE salary set sex = if(sex = ‘m‘,‘f‘,‘m‘);
解法1：
# Write your MySQL query statement below
select
`id`,
max(if(`month` = ‘Jan‘, revenue, null)) as "Jan_Revenue",
max(if(`month` = ‘Feb‘, revenue, null)) as "Feb_Revenue",
max(if(`month` = ‘Mar‘, revenue, null)) as "Mar_Revenue",
max(if(`month` = ‘Apr‘, revenue, null)) as "Apr_Revenue",
max(if(`month` = ‘May‘, revenue, null)) as "May_Revenue",
max(if(`month` = ‘Jun‘, revenue, null)) as "Jun_Revenue",
max(if(`month` = ‘Jul‘, revenue, null)) as "Jul_Revenue",
max(if(`month` = ‘Aug‘, revenue, null)) as "Aug_Revenue",
max(if(`month` = ‘Sep‘, revenue, null)) as "Sep_Revenue",
max(if(`month` = ‘Oct‘, revenue, null)) as "Oct_Revenue",
max(if(`month` = ‘Nov‘, revenue, null)) as "Nov_Revenue",
max(if(`month` = ‘Dec‘, revenue, null)) as "Dec_Revenue"
from
Department
group by `id`;
解法1：连接查询，然后组合两个条件
学到了DATEDIFF是两个日期的天数差集
select a.Id from Weather as a join Weather as b on a.Temperature> b.Temperature and dateDiff(a.RecordDate,b.RecordDate) = 1
select max(Salary) AS SecondHighestSalary from employee where salary < (select max(salary) from employee)
解法1：
# Write your MySQL query statement below
select s.Score,(select count(distinct Score)
from Scores where Score >= s.Score)
as Rank from Scores s
order by s.Score desc
应该是最简单的SQL题：
解法1：
# Write your MySQL query statement below select name,population,area from world where population > 25000000 or area > 3000000;
解法2：
select name,population,area from World where area > 3000000
union
select name,population,area from World where population > 25000000;
解法1:
左连接
# Write your MySQL query statement below select FirstName,LastName,City,State from Person left join Address on Person.PersonId = Address.PersonId
解法1：思路：
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
RETURN (
# Write your MySQL query statement below.
select if(
(select count(*) from (select distinct Salary from Employee) a) < N,
null,
(select Salary as getNthHighestSalary from
(select distinct Salary from Employee order by Salary desc limit N) b
order by Salary asc limit 1)
)
);
END
新知识：
要注意的是：插入数据的表必须有主键或者是唯一索引！否则的话，replace into 会直接插入数据，这将导致表中出现重复的数据。
replace into 跟 insert 功能类似，不同点在于：replace into 首先尝试插入数据到表中， 1. 如果发现表中已经有此行数据（根据主键或者唯一索引判断）则先删除此行数据，然后插入新的数据。 2. 否则，直接插入新数据。
注意：IS NULL 不是 = NULL
解法1：
其实这也产生了笛卡尔乘积
：
# Write your MySQL query statement below
SELECT
a.Name AS ‘Employee‘
FROM
Employee AS a,
Employee AS b
Where
a.ManagerId = b.Id
AND a.Salary > b.Salary
解法2：
使用JOIN
# Write your MySQL query statement below SELECT a.NAME as Employee FROM Employee AS a JOIN Employee AS b ON a.ManagerId = b.Id AND a.Salary > b.Salary
标签：you 行数据 res sts 函数 return div date weather
原文地址：https://www.cnblogs.com/JasonPeng1/p/12234434.html
