MySQL高阶SQL语句（学会这些，让你对于数据库游刃有余）
文章目录
环境准备：
use gcc;
create table location (Region char(20),Store_Name char(20));
insert into location values('East','Boston');
insert into location values('East','New York');
insert into location values('West','Los Angeles');
insert into location values('West','Houston');
select * from location;
location 表格如下:
+--------+-------------+
| Region | Store_Name |
+--------+-------------+
| East | Boston |
| East | New York |
| West | Los Angeles |
| West | Houston |
+--------+-------------+
4 rows in set (0.00 sec)
create table Store_Info (Store_Name char(20),Sales int(10),Date char(10));
insert into Store_Info values('Los Angeles','1500','2020-12-05');
insert into Store_Info values('Houston','250','2020-12-07');
insert into Store_Info values('Los Angeles','300','2020-12-08');
insert into Store_Info values('Boston','700','2020-12-08');
select * from Store_Info;
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Houston | 250 | 2020-12-07 |
| Los Angeles | 300 | 2020-12-08 |
| Boston | 700 | 2020-12-08 |
+-------------+-------+------------+
4 rows in set (0.00 sec)
-----SELECT -------显示表格中一个或数个栏位的所有资料
语法: SELECT "栏位" FROM "表名";
SELECT Store_Name FROM Store_Info;
---- DISTINCT ----不显示重复的资料
语法: SELECT DISTINCT "栏位" FROM "表名";
SELECT DISTINCT Store_Name FROM Store_Info;
-----WHERE-------有条件查询
语法: SELECT "栏位" FROM "表名" WHERE "条件";
SELECT Store_Name FROM Store_Info WHERE Sales > 1000;
-----AND OR -----且 或
语法: SELECT "栏位" FROM "表名" WHERE "条件1" （[AND|OR] "条件2"）+ ;
SELECT Store_Name FROM Store_Info WHERE Sales > 1000 OR (Sales < 500 AND Sales > 200);
----IN-----------显示已知的值的资料
语法: SELECT "栏位" FROM "表名" WHERE "栏位" IN ('值1','值2',...);
SELECT * FROM Store_Info WHERE Store_Name IN ('Los Angeles','Houston');
----BETWEEN------显示两个值范围内的资料
语法: SELECT "栏位" FROM "表名" WHERE "栏位" BETWEEN '值1' AND '值2';
SELECT * FROM Store_Info WHERE Date BETWEEN '2020-12-06' AND '2020-12-10';
------通配符-------通常通配符都是跟 LIKE 一起使用的
% : 百分号表示零个、一个或多个字符
_ : 下划线表示单个字符
'A_Z': 所有以'A'起头，另一个任何值的字符，且以'Z'为结尾的字符串。例如，'ABZ' 和'A2Z'都符合这一个模式，而'AKKZ' 并不符合
'ABC%': 所有以'ABC' 开头的字符串。 例如，'ABCD' 和'ABCABC' 都符合这个模式。
'%XYZ': 所有以'XYZ' 结尾的字符串。 例如，'WXYZ' 和'ZZXYZ' 都符合这个模式。
'%AN%': 所有含有'AN'这个模式的字符串。例如，'LOS ANGELES'和'SAN FRANCISCO' 都符合这个模式。
'_AN%': 所有第二个字母为'A' 和第三个字母为'N' 的字符串。例如，'SAN FRANCISCO' 符合这个模式，而'LOS ANGELES'则不符合这个模式。
------LIKE----匹配一个模式来找出我们要的资料
语法: SELECT "栏位” FROM "表名" WHERE "栏位" LIKE {
模式};
SELECT * FROM Store_Info WHERE Store_Name like '%os%';
---- ORDER BY -----按关键字排序
语法: SELECT "栏位" FROM "表名" [WHERE "条件"] ORDER BY "栏位" [ASC，DESC];
#ASC是按照升序进行排序的，是默认的排序方式。
#DESC是按降序方式进行排序。
SELECT Store_Name,Sales,Date FROM Store_Info ORDER BY Sales DESC;
------------------------函数-------------------------
1、数学函数：
| 函数 | 作用 |
|---|---|
| abs(x) | 返回 x 的绝对值 |
| rand() | 返回 0 到 1 的随机数 |
| mod(x,y) | 返回 x 除以 y 以后的余数 |
| power(x,y) | 返回 x 的 y 次方 |
| round(x) | 返回离 x 最近的整数 |
| round(x,y) | 保留 x 的 y 位小数四舍五入后的值 |
| sqrt(x) | 返回 x 的平方根 |
| truncate(x,y) | 返回数字 x 截断为 y 位小数的值 |
| ceil(x) | 返回大于或等于 x 的最小整数 |
| floor(x) | 返回小于或等于 x 的最大整数 |
| greatest(x1,x2…) | 返回集合中最大的值 |
| least(x1,x2…) | 返回集合中最小的值 |
举例：
SELECT abs(-1),rand(),mod(5,3),power(2,3),round(1.89);
SELECT round(1.8937,3),truncate(1.253,2),ceil(5.2),floor(2.1),least(1.89,3,6.1,3.3);
2、聚合函数：
| 函数 | 作用 |
|---|---|
| avg() | 返回指定列的平均值 |
| count() | 返回指定列中非NULL值的个数 |
| min() | 返回指定列的最小值 |
| max() | 返回指定列的最大值 |
| sum(x) | 返回指定列的所有值之和 |
举例：
SELECT avg(Sales) FROM Store_Info;
SELECT count(Store_Name) FROM Store_Info;
SELECT count(DISTINCT Store_Name) FROM Store_Info; #DISTINCT为不显示重复信息
#count(*) 包括了所有的列的行数，在统计结果的时候，不会忽略列值为NULL（空）的行；
#count(列名) 只包括列名那一行的行数，在统计结果的时候，会忽略列值为NULL（空）的行。
SELECT max(Sales) FROM Store_Info;
SELECT min(Sales) FROM Store_Info;
SELECT sum(Sales) FROM Store_Info;
3、字符串函数：
| 函数 | 作用 |
|---|---|
| trim() | 返回去除指定格式的值 |
| concat(x,y) | 将提供的参数x和y拼接成一个字符串 |
| substr(x,y) | 获取从字符串x中的第y个位置开始的字符串，跟substring() 函数作用相同 |
| substr(x,y,z) | 获取从字符串x中的第y个位置开始长度为z的字符串 |
| length(x) | 返回字符串x的长度 |
| replace(x,y,z) | 用字符串z替代字符串x中的字符串y |
| upper(x) | 将字符串x的所有字母变成大写字母 |
| lower(x) | 将字符串x的所有字母变成小写字母 |
| left(x,y) | 返回字符串x的前y个字符 |
| right(x,y) | 返回字符串x的后y个字符 |
| repeat(x,y) | 将字符串x重复y次 |
| space(x) | 返回x个空格 |
| strcmp(x,y) | 比较x和y，返回的值可以为-1,0,1 |
| reverse(x) | 将字符串x反转 |
举例：
SELECT concat(Region,Store_Name) FROM location WHERE Store_Name ='Boston';
结果如下：
+---------------------------+
| concat(Region,Store_Name) |
+---------------------------+
| EastBoston |
+---------------------------+
1 row in set (0.00 sec)
#如sql_mode开启 开启了PIPES_AS_CONCAT(该模块在/etc/my.cnf中查看是否开启)，"||"视为字符串的连接操作符而非或运算符，和字符串的拼接函数Concat相类似，这和Oracle数据库使用方法一样
SELECT Region || ' ' || Store_Name FROM location WHERE Store_Name = 'Boston';
结果如下：
+-----------------------------+
| Region || ' ' || Store_Name |
+-----------------------------+
| East Boston |
+-----------------------------+
1 row in set (0.00 sec)
SELECT substr(Store_Name,3) FROM location WHERE Store_Name = 'Los Angeles';
SELECT substr(Store_Name,2,4) FROM location WHERE Store_Name = 'New York';
SELECT TRIM ([位置] [要移除的字符串] FROM 字符串);
#[位置]: 值可以为 LEADING (起头)，TRAILING (结尾)，BOTH (起头及结尾)。
#[要移除的字符串]: 从字串的起头、结尾或起头及结尾移除的字符串。缺省时为空格。
SELECT TRIM(LEADING 'Ne' FROM 'New York');
SELECT Region,length(Store_Name) FROM location;
SELECT REPLACE (Region,'ast','astern') FROM location;
------GROUP BY------对GROUP BY后面的栏位的查询结果进行汇总分组，通常是结合聚合函数一起使用的
GROUP BY 有一个原则，就是 SELECT 后面的所有列中，没有使用聚合函数的列，必须出现在GROUPBY后面。
语法: SELECT "栏位1",SUM("栏位2") FROM "表名" GROUP BY "栏位1";
SELECT Store_Name,SUM(Sales) FROM Store_Info GROUP BY Store_Name ORDER BY sales desc;
------- HAVING ----用来过滤由 GROUP BY 语句返回的记录集，通常与 GROUP BY 语句联合使用
HAVING 语句的存在弥补了 WHERE 关键字不能与聚合函数联合使用的不足。如果被 SELECT 的只有函数栏，那就不需要GROUP BY子句。
语法: SELECT "栏位1",SUM("栏位2") FROM "表名" GROUP BY "栏位1" HAVING (函数条件);
SELECT Store_Name,SUM(Sales) FROM Store_Info GROUP BY Store_Name HAVING SUM(Sales) > 1500;
---- ----别名---------栏位別名 表格别名
语法: SELECT "表格别名"."栏位1" [AS] "栏位别名" FROM "表格名" [AS] "表格别名";
SELECT A.Store_Name Store,SUM(A.Sales) "Total Sales" FROM Store_Info A GROUP BY A.Store_Name;
---------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);
SELECT Store_Name,SUM(Sales),COUNT(Sales) FROM Store_Info GROUP BY Store_Name ORDER BY Sales;
+-------------+------------+--------------+
| Store_Name | SUM(Sales) | COUNT(Sales) |
+-------------+------------+--------------+
| Houston | 250 | 1 |
| Boston | 700 | 1 |
| Los Angeles | 1800 | 2 |
+-------------+------------+--------------+
3 rows in set (0.01 sec)
------- 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');
SELECT SUM(Sales) FROM Store_Info WHERE Store_Name IN ('Los Angeles','Houston');
+------------+
| SUM(Sales) |
+------------+
| 2050 |
+------------+
1 row in set (0.00 sec)
--------------连接查询----------------
location 表格如下:
+--------+-------------+
| Region | Store_Name |
+--------+-------------+
| East | Boston |
| East | New York |
| West | Los Angeles |
| West | Houston |
+--------+-------------+
4 rows in set (0.00 sec)
UPDATE Store_Info SET store_name='Washington' WHERE sales=300;
Store_Info 表格如下：
mysql> select * from Store_Info;
+-------------+-------+------------+
| Store_Name | Sales | Date |
+-------------+-------+------------+
| Los Angeles | 1500 | 2020-12-05 |
| Houston | 250 | 2020-12-07 |
| Washington | 300 | 2020-12-08 |
| Boston | 700 | 2020-12-08 |
+-------------+-------+------------+
4 rows in set (0.00 sec)
inner join(等值相连): 只返回两个表中联结字段相等的行
left join(左联接): 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
right join(右联接): 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 INNER JOIN Store_Info B on A.Store_Name = B.Store_Name;
SELECT * FROM location A RIGHT 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;
SELECT A.Region REGION,SUM(B.Sales) SALES FROM location A,Store_Info B WHERE A.Store_Name = B.Store_Name GROUP BY REGION;
-------------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，写的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; #删除视图
------------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
UNION: 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];
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 SELECT Store_Name FROM Store_Info;
SELECT Store_Name FROM location UNION ALL SELECT Store_Name FROM Store_Info;
-------------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);
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 A.Store_Name FROM location A INNER JOIN Store_Info B ON A.Store_Name = B.Store_Name) A
GROUP BY A.Store_Name HAVING COUNT(*) >= 1;
SELECT DISTINCT A.Store_Name FROM location A INNER JOIN Store_Info B USING(Store_Name); _Name);
--------------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;
----------- 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
END
"New Sales", Date
FROM Store_Info;
#"New sales" 是用于 CASE 那个栏位的栏位名
#创建一个新表：
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);
Total_Sales 表格如下:
mysql> select * from Total_Sales;
+----------+-------+
| Name | Sales |
+----------+-------+
| zhangsan | 10 |
| lisi | 15 |
| wangwu | 20 |
| zhaoliu | 40 |
| sunqi | 50 |
| zhouba | 20 |
| wujiu | 30 |
+----------+-------+
7 rows in set (0.00 sec)
-------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(包含那一行本身)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栏位的值是比自已本身的值小的以及sales栏位和Name栏位都相同的数量，比如zhangsan为5+1=6
----------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
-------- 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;
---------算总合百分比--------------
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
--------算累积总合百分比--------------
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;
#用累积总计SUM(a2.sales) 除以总合来求出每一行的累积总合百分比.
SELECT A1.Name,A1.sales,TRUNCATE(ROUND(SUM(A2.Sales)/(SELECT SUM(Sales) FROM Total_Sales),4)*100,2) || '%' 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;