young
- mysql-sql 语句
- 字符集选utf-8
- 我需要学增删改查, 事物, 联合
启动数据库
mysql -u root -p（root是用户名）
查看数据库（所有）
show databases
进入数据库
use one ;
展示当前数据库的所有表
show tables;
创建个名为user的表的结构
create table user(
id int,
name varchar(30),
pass varchar(30)
);（字符串长度最长是30）
查看表结构
desc user;
查看数据从表里面
select * from user;
insert 增（我可以随意增加，插入数据到表中）
insert into table(ct1,ct2,ct3) values(num,"str","str")
insert into user(id,name,pass) values(1,"leiwei","123")
形成了下表
mysql> select * from user;
+------+-----------+------+
| id | name | pass |
+------+-----------+------+
| 1 | leiwei | 123 |
| 2 | yujie | 13 |
| 3 | qiancheng | 456 |
+------+-----------+------+
3 rows in set (0.00 sec)
select 查（我可以随意查找 select from table where...）
select * from user where id=2;
select * from user where pass=13;
select like 子段（ 我可以随意选取子字段 ）
select * from user where name like '%carry%';//选取中间含有carry字段的数据
+------+----------+------+
| id | name | pass |
+------+----------+------+
| 5 | carryone | 123 |
| 2 | carry | 571 |
+------+----------+------+
选取以one结束的字段
select * from user where name like '%one';//
+------+----------+------+
| id | name | pass |
+------+----------+------+
| 5 | carryone | 123 |
+------+----------+------+
select order by 排序（我们可以随意排序数据）
select * from user order by name; //默认是升序
select * from user order by id desc;//desc为降序排列
delete 删 （我可以随意删除 delete from table where...）
delete from user where name="yujie";
delete from user where id=3;
update (我可以随意更改 update user set charct where ....)
update user set name="billin" where id=1;
update user set id=5 where name="billin";
inner/left/right join 联合，内联，左联，右联
select a.pass,b.money from user a left join customer b on a.name = b.name;//左连
select a.pass,a.name,b.money from user a right join customer b on a.id = b.id;//左联
select a.pass,a.name,b.money from user a inner join customer b on a.name = b.name;//内联
常用语句(联合)
SELECT
gbl_products.productName,
gbl_stocks.areaID,
gbl_stocks.amounts,
gbl_stocks.stocks_standard,
gbl_product_barcodes.barcode,
gbl_md5.image
FROM
gbl_products
LEFT JOIN gbl_stocks ON gbl_products.id = gbl_stocks.productID
LEFT JOIN gbl_product_barcodes ON gbl_products.id = gbl_product_barcodes.productID
LEFT JOIN gbl_md5 ON gbl_products.productImage = gbl_md5.md5
WHERE
gbl_stocks.amounts <= (
gbl_stocks.stocks_standard / 2
);
实现的效果
lala
切记
1:from 后面跟一个表的名字，且这个表为主表
2: （ON DUPLICATE KEY UPDATE） 查看有没有，没有就插入，有就更新
INSERT INTO gbl_stocks (
gbl_stocks.productID,
gbl_stocks.areaID,
gbl_stocks.amounts,
gbl_stocks.stocks_standard
)
VALUES
(?,?,?,?) ON DUPLICATE KEY UPDATE gbl_stocks.amounts = gbl_stocks.amounts +VALUES(gbl_stocks.amounts),
gbl_stocks.stocks_standard =
`IF` (
gbl_stocks.amounts +VALUES(gbl_stocks.amounts) > gbl_stocks.stocks_standard,gbl_stocks.amounts +VALUES(gbl_stocks.amounts),gbl_stocks.stocks_standard
)
VALUES(gbl_stocks.amounts)中,括号里面是一个可变化的动态的值，一般为读取到的值
判断
if(a> b,c,d);
意思为：
如果条件成立（a>b）,则返回c,反之返回d
主键
主键是一个表中具有唯一标识性的字段，其它的属性字段都根据主键来存在的，例如学号
外键
mysql-外键：表A和表B都有一个相同的字段c，c是表A的主键，c不是表B 的主键，表B的字段c相对于表A是表B的外键
希望有更多小胖友提出宝贵意见,若有关于前端的问题，或者关于大学方面的感想可以私聊我(~)：
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