修改 数据库.md

Miller-Xie · Miller-Xie · commit 3b210bd90bc1 · 2019-03-02T11:36:37.000+08:00
diff --git a/LeetCode/数据库.md b/LeetCode/数据库.md
@@ -503,7 +503,18 @@ select class from courses group by class having count(distinct student) >= 5;
 ### 解答
 
 ```mysql
+# Write your MySQL query statement below
+select max(Salary) as SecondHighestSalary from Employee 
+where Salary < (select max(Salary) from Employee);
+```
+
 
+
+
+```mysql
+# Write your MySQL query statement below
+select 
+ifnull((select distinct salary from employee order by salary desc limit 1,1),null) as SecondHighestSalary;
 ```
 
 
@@ -520,8 +531,6 @@ select class from courses group by class having count(distinct student) >= 5;
 
 你能不能帮她写一个 SQL query 来输出小美想要的结果呢？
 
- 
-
 **示例：**
 
 ```
@@ -557,7 +566,31 @@ select class from courses group by class having count(distinct student) >= 5;
 ### 解答
 
 ```mysql
+# Write your MySQL query statement below
+select (
+case 
+    when id % 2 = 0 then id-1
+    when id % 2 = 1 and id != (select count(*) from seat) then id+1
+    else id
+end
+) as id,
+student
+from seat order by id;
+```
 
+
+
+```mysql
+# Write your MySQL query statement below
+select * from
+(
+select id-1 as id,student from seat where mod(id,2) = 0
+union
+select id+1 as id,student from seat where mod(id,2) = 1 and id !=(select count(*) from seat)
+union
+select id,student from seat where mod(id,2) = 1 and id = (select count(*) from seat)
+) as temp 
+order by id;
 ```
 
 
@@ -599,6 +632,18 @@ select class from courses group by class having count(distinct student) >= 5;
 ### 解答
 
 ```mysql
+# Write your MySQL query statement below
+select a.Score,(select count(distinct b.Score) from Scores as b where b.Score >= a.Score) as Rank
+from Scores as a
+order by Rank;
+```
+
+
 
+```mysql
+# Write your MySQL query statement below
+select a.Score,(select count(distinct b.Score) from Scores as b where b.Score >= a.Score) as Rank
+from Scores as a
+order by Score desc;
 ```
 
