1.登陆数据库的指令mysql -uroot -pmysql
通过标记选中语句–》右键复制—》右键粘贴
2.创建数据表
语法:
create table table_name (column_name1 column_type1[, column_name2 column_type2[, …]] )
说明:
table_name 表名
column_name1, column_name2, … 字段名
column_type1, column_type2, … 字段类型
3.修改表结构
添加字段 alter table 表名 add type char(5) unique after name;
4.条件查找 > < >= <= = !=
SELECT * FROM goods WHERE price = 5
SELECT * FROM goods WHERE price !=5
5.范围查找 and or
SELECT * FROM goods WHERE price <10 OR TYPE=‘饮品’
SELECT * FROM goods WHERE price <10 AND TYPE=‘饮品’
//BETWEEN 10 AND 50
SELECT * FROM goods WHERE price BETWEEN 10 AND 50
//NOT BETWEEN 10 AND 50
SELECT * FROM goods WHERE price NOT BETWEEN 10 AND 50
//in
SELECT * FROM goods WHERE price IN(2,5,23)
// not in
SELECT * FROM goods WHERE price NOT IN(2,5,23)
6.聚合函数:只能查找被聚合的列
最小值:min() SELECT MIN(price),NAME FROM goods
最大值:max() SELECT MAX(price) FROM goods
求和:sum() SELECT SUM(price) FROM goods
计数:count() SELECT COUNT(price) FROM goods
平均值:avg() select avg(price) from goods
7.排序:
正序:默认的 ASC SELECT * FROM goods ORDER BY price ASC
倒序: DESC SELECT * FROM goods ORDER BY price DESC
8.模糊查询 like %
查找带可字的商品
以可开头,结尾不知道 SELECT * FROM goods WHERE NAME LIKE ‘可%’
以可结尾,开头不知道 SELECT * FROM goods WHERE NAME LIKE ‘%可’
可在中间,前后都不知道 SELECT * FROM goods WHERE NAME LIKE ‘%可%’
可字能确定位置 SELECT * FROM goods WHERE NAME LIKE ‘_可%’ 第二个字是可
9.提取一部分数据
limit 第一个参数,第二个参数 第一个参数:起始位置 从0开始 第二个参数:查几条
select * from goods limit 0,3
例:查询表中第3条~第7条记录的值
select * from t1 limit 3, 5
注意:第3条~第7条记录为3、4、5、6、7,所以limit从第3条记录开始获取信息,取出5条记录。
10.分组 group by
SELECT TYPE,COUNT(*) FROM goods GROUP BY TYPE
11.查找重名记录
SELECT NAME,COUNT( * ) FROM goods GROUP BY NAME HAVING COUNT( * )>1
having和where 的区别:
having是后条件,作用在临时表,查询结果
where 是前条件,作用在原始表
12.Is是指定查询条件包含的字段是否为空值时使用的关键字:
如果条件是null 用is
SELECT * FROM goods WHERE TYPE IS NULL
13.添加记录
语法:
insert into table_name (column_name1[, column_name2[, …]]) values (column_value1[, column_value2[, …]] )
说明:
table_name 表名
column_name1, column_name2, … 字段名
column_value1, column_value2, … 字段存储的值
14.删除记录
语法:
delete from table_name where column_name1 = column_value1 [ and | or column_name2 = column_value2[ and | or …]]
说明:
table_name 表名
column_name1 删除记录依据的字段名
column_value1 删除记录依据的字段值
and 表示与(同时满足条件的记录)
or 表示或(部分满足条件的记录)
15.修改记录
语法:
update table_name set column_name1 = column_value1 [, column_name2 = column_value2[, …]] where column_name3 = column_value3[ and | or column_name4 = column_value4[ and | or …]]
说明:
table_name 表名
column_name1, column_name2, … 字段名
column_value1, column_value2, … 要修改成的字段值
column_name3, column_name4, … 修改记录依据的字段名
column_value3, column_value4, … 修改记录依据的字段值
and 表示与(同时满足条件的记录)or 表示或(部分满足条件的记录)