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; mysql> select Region,length(Store_name) from location; +--------+
--------------------+ | Region | length(Store_name) | +--------+
--------------------+ | East | 6 | | East | 8 | | West | 11 | | West | 7 | +
--------+--------------------+ 4 rows in set (0.00 sec) 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; mysql> select Store_Name,sum(Sales) from Store_Info group by
Store_Name order by sales desc; +-------------+------------+ | Store_Name | sum(
Sales) | +-------------+------------+ | Houston | 250 | | Washington | 300 | |
Boston | 700 | | Los Angeles | 1500 | +-------------+------------+ 4 rows in set
(0.00 sec) ------- 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;
mysql> SELECT * FROM location A INNER JOIN Store_Info B on A.Store_Name = B.
Store_Name; +--------+-------------+-------------+-------+------------+ | Region
| Store_Name | Store_Name | Sales | Date | +--------+-------------+-------------
+-------+------------+ | West | Los Angeles | Los Angeles | 1500 | 2020-12-05 |
| West | Houston | Houston | 250 | 2020-12-07 | | East | Boston | Boston | 700 |
2020-12-08 | +--------+-------------+-------------+-------+------------+ 3 rows
in set (0.00 sec) 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 +----------+-------
+------+ | Name | Sales | Rank | +----------+-------+------+ | sunqi | 50 | 1 |
| zhaoliu | 40 | 2 | | wujiu | 30 | 3 | | wangwu | 20 | 4 | | zhouba | 20 | 4 |
| lisi | 15 | 6 | | zhangsan | 10 | 7 | +----------+-------+------+ 7 rows in
set (0.00 sec) ----------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 +--------+ |
Middle | +--------+ | 20 | +--------+ 1 row in set (0.00 sec) --------
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; +----------+-------+-----------+ | Name | Sales |
Sum_Total | +----------+-------+-----------+ | sunqi | 50 | 50 | | zhaoliu | 40
| 90 | | wujiu | 30 | 120 | | zhouba | 20 | 140 | | wangwu | 20 | 140 | | lisi |
15 | 175 | | zhangsan | 10 | 185 | +----------+-------+-----------+ 7 rows in
set (0.00 sec) ---------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 +----------+-------+-----------
+ | Name | Sales | Per_Total | +----------+-------+-----------+ | sunqi | 50 |
0.2703 | | zhaoliu | 40 | 0.2162 | | wujiu | 30 | 0.1622 | | zhouba | 20 |
0.1081 | | wangwu | 20 | 0.1081 | | lisi | 15 | 0.0811 | | zhangsan | 10 |
0.0541 | +----------+-------+-----------+ 7 rows in set (0.00 sec)
--------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; +----------+-------+-----------+ | Name | Sales
| Per_Total | +----------+-------+-----------+ | sunqi | 50 | 0.2703 | | zhaoliu
| 40 | 0.4865 | | wujiu | 30 | 0.6486 | | zhouba | 20 | 0.7568 | | wangwu | 20 |
0.7568 | | lisi | 15 | 0.9459 | | zhangsan | 10 | 1.0000 | +----------+-------+
-----------+ 7 rows in set (0.00 sec) #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; +----------+-------+-----------+ | Name |
sales | Per_Total | +----------+-------+-----------+ | sunqi | 50 | 27.03% | |
zhaoliu | 40 | 48.65% | | wujiu | 30 | 64.86% | | zhouba | 20 | 75.68% | |
wangwu | 20 | 75.68% | | lisi | 15 | 94.59% | | zhangsan | 10 | 100.00% | +
----------+-------+-----------+ 7 rows in set (0.00 sec) --------- 空值(NULL) 和无值(
'')的区别--------- 1.无值的长度为0,不占用空间的; 而NULL值的长度是NULL,是占用空间的。 2. Is NULL或者Is NOT
NULL,是用来判断字段是不是为NULL或者不是NULL,不能查出是不是无值的。 3.无值的判断使用 ='' 或者 <>'' 来处理。 <>代表不等于。 4.
在通过 count()指定字段统计有多少行数时,如果遇到NULL 值会自动忽略掉,遇到无值会加入到记录中进行计算。 创建City表格: use gcc;
create table city (name char(10)); insert into city values('beijing'); insert
into city values('nanjing'); insert into city values('shanghai'); insert into
city values(); insert into city values(); insert into city values(); insert into
city values(''); insert into city values(''); mysql> select * from city; +
----------+ | name | +----------+ | beijing | | nanjing | | shanghai | | NULL |
| NULL | | NULL | | | | | +----------+ SELECT length (NULL),length(''),length(
'1'); +---------------+------------+-------------+ | length (NULL) | length('')
| length('1') | +---------------+------------+-------------+ | NULL | 0 | 1 | +
---------------+------------+-------------+ 1 row in set (0.00 sec) SELECT *
FROM city WHERE name IS NULL; #不会把无值计算进去 SELECT * FROM city WHERE name IS NOT
NULL; #会把无值也计算进去 SELECT * FROM city WHERE name = ''; SELECT * FROM city WHERE
name <> ''; SELECT COUNT(*) FROM city; #空值和无值都会计算进去 SELECT COUNT(name) FROM city
; #忽略空值,但是会把无值计算进去 -------------正则表达式------------------ 匹配模式 描述 实例 ^ 匹配文本的开始字符 ‘
^bd’ 匹配以 bd 开头的字符串 $ 匹配文本的结束字符 ‘qn$’ 匹配以 qn 结尾的字符串 . 匹配任何单个字符 ‘s.t’ 匹配任何 s 和 t
之间有一个字符的字符串 * 匹配零个或多个在它前面的字符 ‘fo*t’ 匹配 t 前面有任意个 o + 匹配前面的字符 1 次或多次 ‘hom+’ 匹配以 ho
开头,后面至少一个m 的字符串 字符串 匹配包含指定的字符串 ‘clo’ 匹配含有 clo 的字符串 p1|p2 匹配 p1 或 p2 ‘bg|fg’ 匹配
bg 或者 fg [...] 匹配字符集合中的任意一个字符 ‘[abc]’ 匹配 a 或者 b 或者 c [^...] 匹配不在括号中的任何字符 ‘[^ab]’
匹配不包含 a 或者 b 的字符串 {n} 匹配前面的字符串 n 次 ‘g{2}’ 匹配含有 2 个 g 的字符串 {n,m} 匹配前面的字符串至少 n
次,至多m 次 ‘f{1,3}’ 匹配 f 最少 1 次,最多 3 次 语法: SELECT "栏位” FROM "表名" WHERE "栏位" REGEXP
{模式}; SELECT * FROM Store_Info WHERE Store_Name REGEXP 'os'; #匹配包含os的字符串 SELECT
* FROM Store_Info WHERE Store_Name REGEXP '^[A-G]'; #匹配以A-G开头的字符串 SELECT * FROM
Store_Info WHERE Store_Name REGEXP 'Ho|Bo'; #匹配具有Ho或Bo的字符串
-------------存储过程---------------- 1、存储过程是一组为了完成特定功能的SQL语句集合。 2
、存储过程在使用过程中是将常用或者复杂的工作预先使用SQL语句写好并用一个指定的名称存储起来,这个过程经编译和优化后存储在数据库服务器中。当需要使用该存储过程时,只需要调用它即可。存储过程在执行上比传统SQL速度更快、执行效率更高。
3、存储过程的优点: (1)执行一次后,会将生成的二进制代码驻留缓冲区,提高执行效率 (2)SQL语句加上控制语句的集合,灵活性高 (3
)在服务器端存储,客户端调用时,降低网络负载 (4)可多次重复被调用,可随时修改,不影响客户端调用 (5)可完成所有的数据库操作,也可控制数据库的信息访问权限
##创建存储过程## DELIMITER $$ #将语句的结束符号从分号;临时改为两个$$(可以是自定义) CREATE PROCEDURE Proc() #
创建存储过程,过程名为Proc,不带参数 -> BEGIN #过程体以关键字 BEGIN 开始 -> select * from Store_Info; #
过程体语句 -> END $$ #过程体以关键字 END 结束 DELIMITER ; #将语句的结束符号恢复为分号 ##调用存储过程## CALL Proc;
##查看存储过程## SHOW CREATE PROCEDURE [数据库.]存储过程名; #查看某个存储过程的具体信息 SHOW CREATE
PROCEDURE Proc; SHOW PROCEDURE STATUS [LIKE '%Proc%'] \G ##存储过程的参数## IN
输入参数:表示调用者向过程传入值(传入值可以是字面量或变量) OUT 输出参数:表示过程向调用者传出值(可以返回多个值)(传出值只能是变量) INOUT
输入输出参数:既表示调用者向过程传入值,又表示过程向调用者传出值(值只能是变量) 举例: DELIMITER $$ CREATE PROCEDURE Proc1
(IN inname CHAR(16)) -> BEGIN -> SELECT * FROM Store_Info WHERE Store_Name =
inname; -> END $$ DELIMITER ; CALL Proc1('Boston'); ##删除存储过程##
存储过程内容的修改方法是通过删除原有存储过程,之后再以相同的名称创建新的存储过程。 DROP PROCEDURE IF EXISTS Proc; ##
存储过程的控制语句## create table t (id int(10)); insert into t values(10); (1)
条件语句if-then-else-end if DELIMITER $$ CREATE PROCEDURE proc2(IN parameter int) ->
begin -> declare var int; -> set var=parameter*2; -> if var>=10 then -> update t
set id=id+1; -> else -> update t set id=id-1; -> end if; -> end $$ DELIMITER ;
CALL Proc2(6); (2)循环语句while ···· end while DELIMITER $$ CREATE PROCEDURE proc3()
-> begin -> declare var int(10); -> set var=0; -> while var<6 do -> insert into
t values(var); -> set var=var+1; -> end while; -> end $$ DELIMITER ; CALL Proc3;

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