MySQL高级语句|进阶语句|select语句（二）【图文细解】

一、select语句

1、别名

栏位别名表格別名

语法: SELECT "表格别名". "栏位1" [AS] "栏位别名”FROM "表格名" [AS] "表格别名";    #AS可省略
SELECT A.Store_Name Store,SUM(A.Sales) "Total Sales" FROM Store_Info A GROUP BY A.Store_Name;

2、子查询

连接表格，在WHERE 子句或HAVING 子句中插入另一个SQL 语句

语法: SELECT "栏位1" FROM "表格1" WHERE "栏位2”[比较运算符]			#外查询
(SELECT "栏位1" FROM "表格2" WHERE "条件");						#内查询

#可以是符号的运算符，例如=、>、<. >=、<= ; 也可以是文字的运算符，例如LIKE、 IN、BETWEEN
SELECT SUM(Sales) FROM Store_Info WHERE Store_Name IN
(SELECT Store_Name FROM location WHERE Region = 'West');

SELECT SUM(A.Sales) FROM Store_Info A WHERE A.Store_Name IN
(SELECT Store_Name FROM location B WHERE B.Store_Name = A.Store_Name);

3、EXISTS

用来测试内查询有没有产生任何结果，类似布尔值是否为真

#如果有的话，系统就会执行外查询中的SQL语句。若是没有的话，那整个SQL 语句就不会产生任何结果。

语法: SELECT "栏位1”FROM “表格1" WHERE EXISTS (SELECT * FROM "表格2" WHERE "条件");
SELECT SUM(Sales) FROM Store_Info WHERE EXISTS (SELECT * FROM location WHERE Region = 'West');

4、连接查询

（1）inner join (内连接)

只返回两个表中联结字段相等的行

SELECT * FROM location A INNER JOIN Store_Info B on A.Store_Name = B.Store_Name;

（2）left join (左连接)

返回包括左表中的所有记录和右表中联结字段相等的记录

SELECT * FROM location A left JOIN Store_Info B on A.Store_Name = B.Store_Name;
SELECT * FROM location A, Store_Info B WHERE A.Store_Name = B.Store_Name;

（3）right join (右连接)

返回包括右表中的所有记录和左表中联结字段相等的记录

SELECT * FROM location A right JOIN Store_Info B on A.Store_Name = B.Store_Name;

5、CREATE VIEW ----视图

可以被当作是虚拟表或存储查询

●视图跟表格的不同是，表格中有实际储存资料，而视图是建立在表格之上的一个架构，它本身并不实际储存资料。

●临时表在用户退出或同数据库的连接断开后就自动消失了，而视图不会消失。

●视图不含有数据，只存储它的定义，它的用途一.般可以简化复杂的查询。比如你要对几个表进行连接查询，而且还要进行统计排序等操作，写SQL语句会很麻烦的，用视图将几个表联结起来，然后对这个视图进行查询操作，就和对一个表查询一样，很方便。

语法: CREATE VIEW "视图表名" AS "SELECT 语句";
CREATE VIEW V_REGION SALES AS SELECT A.Region REGION,SUM(B.Sales) SALES FROM location A
INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name GROUP BY REGION;

SELECT * FROM V_REGION_SALES;
DROP VIEW V_REGION_SALES;

6、UNION ----联集

将两个SQL语句的结果合并起来，两个SQL语句所产生的栏位需要是同样的资料种类

ONION

生成结果的资料值将没有重复，且按照字段的顺序进行排序

语法:[SELECT语句1] UNION [SELECT 语句2];

select Store_Name FROM location UNION select Store_Name FROM Store_Info;

UNION ALL

将生成结果的资料值都列出来，无论有无重复

语法: [SELECT 语句1] UNION ALL [SELECT 语句2];

select Store_Name FROM location UNION ALL select Store_Name FROM Store_Info;

7、交集值

取两个sQL语句结果的交集

SELECT A.Store_Name FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name;
SELECT A.Store_Name FROM location A INNER JOIN Store_Info B USING (Store_Name);

#两表其中的一个表没用单独重复的行，而另一个表有重复行，并且要求两个表确实有交集行的时候用
SELECT A.Store_Name FROM
(SELECT store_Name FROM location UNION ALL SELECT Store_Name FROM Store_Info) A
GROUP BY A.Store_Name HAVING COUNT(*) > 1;

#取两个SQL语句结果的交集，且没有重复
SELECT A.Store_Name FROM (SELECT B.Store_Name FROM location B INNER JOIN Store_Info C ON B.Store_Name =C.store_Name) A
GROUP HY A.store_Name;

SELECT DISTINCT A.Store_Name FROM location A INNER JOIN Store_Info B USING(Store_Name);
SELECT DISTINCT Store_Name FROM location WHERE (Store_Name) IN (SELECT store_Name FROM Store_Info);
SELECT DISTINCT A.Store_Name FROM location A LEFT JOIN store_Info B USING(Store_Name) WHERE B.Store_Name IS NOT NULL;

8、无交集值

显示第一个SQL语句的结果，且与第二个sQL语句没有交集的结果，且没有重复

SELECT DISTINCT Store_Name FROM location WHERE (Store_Name) NOT IN (SELECT Store_Name FROM Store_Info);

SELECT DISTINCT A.Store_Name FROM location A LEFT JOIN Store_Info B USING(Store_Name) WHERE B.Store_Name IS NULL;

9、CASE

是SQL用来做为IF-THEN-ELSE 之类逻辑的关键字

语法:
SELECT CASE ("栏位 名")
	WHEN "条件1" THEN "结果1"
	WHEN "条件2” THEN "结果2"
	......
	[ELSE "结果N"]
	END
FROM "表名";
# "条件"可以是一一个数值或是公式。 ELSE 子句则并不是必须的。

SELECT Store_Name,CASE Store_Name
	WHEN 'Los Angeles' THEN Sales * 2
	WHEN 'Boston' THEN Sales * 1.5
	ELSE Sales * 1.5
	END
"New Sales",Date
FROM Store_Info;

#"New Sales"是用于 CASE 那个栏位的栏位名。

二、排序

准备一张新表

CREATE TABLE Total_Sales (Name char(10),Sales int(5));
INSERT INTO Total_Sales VALUES ('zhangsan',10);
INSERT INTO Total_Sales VALUES ('lisi',15);
INSERT INTO Total_Sales VALUES ('wangwu',20);
INSERT INTO Total_Sales VALUES ('zhaoliu',40);
INSERT INTO Total_Sales VALUES ('sunqi',50);
INSERT INTO Total_Sales VALUES ('zhouba',20);
INSERT INTO Total_Sales VALUES ('wujiu',30) ;

1、算排名

表格自我连结(Self Join)， 然后将结果依序列出，算出每一-行之前(包含那- -行本身)有多少行数

SELECT A1.Name, A1.Sales, COUNT (A2.Sales) Rank FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name, A1.Sales ORDER BY A1.Sales DESC;

#统计Sales栏位的值是比自己本身的值小的以及Sales栏位和Name栏位都相同的数量，比如zhangsan为6+1-7

2、算中位数

SELECT Sales Middle FROM (SELECT A1.Name, A1.Sales, COUNT(A2.Sales) Rank FROM Total_Sales A1, Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales = A2.Sales AND A1.Name >= A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC) A3
WHERE A3.Rank = (SELECT (COUNT(*) +1) DIV 2 FROM Total_Sales);

#每个派生表必须有自己的别名，所以别名A3必须要有
#DIV 是在MySQL 中算出商的方式

3、算累积总计

表格自我连结(Self Join)， 然后将结果依序列出，算出每一行之前(包含那一行本身)的总合

SELECT A1.Name,A1.Sales,SUM(A2.Sales) Sum_Total FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;

4、算总分百分比

SELECT A1.Name,A1.Sales,A1.Sales/(SELECT SUM(Sales) FROM Total_Sales) Per_Total
FROM Total_Sales A1,Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales AND A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;

#SELECT SUM(Sales) FROM Total_Sales 这一段子查询是用来算出总合
#总合算出后，我们就能够将每一行一一除以总合来求出每一行的总合百分比

5、算累计百分比

SELECT A1.Name,A1.Sales, SUM(A2.Sales)/(SELECT SUM(Sales) FROM Total_Sales) Per_Total
FROM Total_Sales A1, Total_Sales A2
WHERE A1.Sales < A2.Sales OR (A1.Sales=A2.Sales and A1.Name = A2.Name)
GROUP BY A1.Name,A1.Sales ORDER BY A1.Sales DESC;