MySQL基础语法

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注:表名和列名尽量避免使用MySQL关键字

一、常用SQL语句

1.DDL语句

create

alter

drop

# 创建数据库
create database e_mall;

# 删除数据库
drop database e_mall;

# 创建表
create table if not exists `product_order`(
`id` bigint(20) unsigned auto_increment,
`product_id` bigint(20) unsigned not null comment '产品id',
`count` int unsigned not null comment '购买数量',
`amount` decimal(10,2) not null comment '总价格',
`create_time` datetime not null comment '下单时间',
`modified_time` datetime default null comment '修改时间',
primary key (`id`)
)engine=InnoDB default charset=utf8mb4;

# 查看表信息
desc product_order;
# 查看创建语句
show create table product\G

# 删除表: drop
drop table product_order;

# 修改表: alter
# 添加列: add
alter table product_order add column user_id bigint(20) unsigned not null comment '用户id' after id;
# 删除列: drop
alter table product_order drop column user_id;
# 修改列定义: modify
alter table product_order modify amount decimal(10,2) not null comment '总价(元)';
# 修改列定义及列名: change
alter table product_order change count quantity int unsigned not null comment '购买数量';
# 添加普通索引: add index
alter table product_order add index idx_product_id (`product_id`);
# 删除普通索引: drop index
alter table product_order drop index idx_product_id;
# 添加唯一索引
alter table product_order add unique (`order_serial`);
# 修改表名: alter table rename
alter table product_order rename product_orders;
# 跨库修改表名: rename table to
rename table e_mall_2.product to e_mall_0.product;

2.DML语句

insert

update

delete

select

# 插入记录: insert
insert into product_order(product_id, quantity, amount, create_time) values (3, 1, 7388.00, now());
# insert select语句
insert into product_order(product_id, quantity, amount, create_time)
  select id, 2, 2*price, now() from product where id = 1;

# 更新记录: (join) update
update product_order o join product p on o.product_id = p.id
  set o.quantity = 5, amount = 5*p.price where o.id = 1;

# 删除记录: delete
delete from product_order where id = 10;
# 删除表中所有数据: truncate, 与不带where条件的delete效果相同, 需要事务资源少, 速度快
# delete是DML语句, truncate是DDL语句
truncate table product_order;

# 查询记录
select * from product_order where quantity > 0 order by amount desc limit 1, 1;\
# 聚合查询: group by [having], having关键字对分类后的结果再进行过滤
select product_id, count(1) as order_count, sum(quantity) as total_quantity, sum(amount) as total_amount
  from product_order where quantity > 0 group by product_id having total_quantity > 2;

# 表连接查询: join
# 全连接: full join
select * from product full join product_order;
# 查询多表的全连接
select * from product, product_order;
# 子连接: in, not in, =, !=, exists, not exists
# in查询: 索引用在product_order, 与exists的区别在于索引作用的表不同
select * from product_order where product_id in (select id from product);
# exists条件查询: 当能返回结果集则为1, 不能返回结果集则为0; 索引用在product表
select * from product_order where exists (select * from product where product.id = product_order.product_id);

3.DCL语句

grant

# 用户授权
grant select,insert on e_mall.* to 'test_user'@'%' identified by 'Dev!@#123' with grant option;
# 帮助使用: ? Xxx
# 查看所有的show命令
? show

二、数据类型

1.数值类型

2.日期类型

3.字符串类型

4.枚举类型和SET类型

# 创建表
create table if not exists `member` (
`id` int unsigned auto_increment,
`gender` enum('M','F') not null,
`hobby` set('running','movie','music') not null,
primary key (`id`)
)engine=InnoDB default charset=utf8mb4;

# 插入记录: 枚举类型只能从集合中选取单个值, SET类型可以一次选取多个成员
insert into member(gender, hobby) values ('M', 'running,movie');

三、运算符

1.算术运算符

2.比较运算符

3.逻辑运算符

4.位运算符

5.运算的优先级

四、常用函数

1.字符串函数

2.数值函数

3.日期和时间函数

时间日期格式符

4.聚合函数

5.流程函数

6.其他常用函数

五、视图、存储过程和触发器

1.视图

# 创建视图: create view ... as ...
create or replace view order_view as
  select o.order_serial, o.product_id, p.name as product_name, o.quantity, o.amount
  from product_order o inner join product p on o.product_id = o.id;
# 修改视图: alter view ... as ...
alter view order_view as
  select o.order_serial, o.product_id, p.name as product_name, o.quantity, o.amount
  from product_order o inner join product p on o.product_id = p.id;
# 查询视图: select
select * from order_view;
# 删除视图: drop view
drop view order_view;

2.存储过程

1).创建存储过程示例:

# 存储过程
# 将结束符改为"$$"
DELIMITER $$
# 创建存储过程: 入参: product_id, user_id, 出参: handle_result
CREATE PROCEDURE purchase_product(IN p_product_id BIGINT(20), IN p_user_id BIGINT(20), OUT p_handle_result TINYINT(1))
# 指定用创建者(DEFINER)还是调用者(INVOKER)的许可来执行
SQL SECURITY DEFINER
# 存储过程开始
BEGIN
    # DECLARE声明顺序: 变量, 条件, 光标, 处理程序
    # ----- 定义变量: 定义变量要在定义条件之前
    DECLARE handle_result TINYINT(1) DEFAULT 0;
    # 订单金额
    DECLARE order_amount DECIMAL(10,2) DEFAULT 0.0;
    # ----- 定义条件: 主键冲突, declare cond_name condition for ...
    DECLARE duplicate_key_cond CONDITION FOR sqlstate '23000';
    # ----- 定义条件处理: declare handle_type(CONTINUE:继续, EXIT:退出) handler for ...
    DECLARE CONTINUE HANDLER FOR duplicate_key_cond SET handle_result = -1;
    # 处理SQL异常
    DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET handle_result = -2;
    # 开始事务
    START TRANSACTION;
    # 查询商品价格并设为订单金额
    SELECT price from product where id = p_product_id INTO order_amount;
    # 插入订单表
    INSERT INTO product_order (order_serial, product_id, user_id, quantity, amount ,create_time)
      VALUES (REPLACE(UUID(),"-",""), p_product_id, p_user_id, 1, order_amount, now());
    # 更新库存
    UPDATE product SET stock = stock - 1 WHERE id = p_product_id and stock > 1;
    # 事务提交或回滚
    IF handle_result 

2).常用操作

# 1.调用存储过程
call purchase_product(3,1,@r);
# 查看结果@r
select @r;
# 2.查看存储过程创建语句
show create procedure purchase_product;
# 3.删除存储过程
drop procedure purchase_product;

3.函数(类似存储过程): BEGIN ... END

# 创建函数: 计算所有商品的价值, 只有入参, 因此不需要IN和OUT标识
CREATE FUNCTION get_product_amount(p_status TINYINT(1))
# 定义返回值类型
RETURNS DECIMAL(10,2)
# 定义模式
DETERMINISTIC
READS SQL DATA
# 函数开始
BEGIN
    # 定义总价值变量
    DECLARE v_product_amount DECIMAL(10,2);
    # 定义临时变量v_price, v_stock用于计算
    DECLARE v_price DECIMAL(10,2);
    DECLARE v_stock INT;
    # ----- 定义光标: DECLARE cursor_name CURSOR FOR select_statement
    DECLARE product_list CURSOR FOR SELECT price, stock FROM product WHERE status = p_status;
    # ----- 定义错误处理器, 出错时关闭光标
    DECLARE EXIT HANDLER FOR SQLEXCEPTION CLOSE product_list;
    # 商品总价值赋初值
    SET v_product_amount = 0;
    # 开启光标进行计算
    OPEN product_list;
    # LOOP循环处理
    outer:LOOP
        FETCH product_list INTO v_price, v_stock;
            SET v_product_amount = v_product_amount + v_price * v_stock;
    END LOOP outer;
    # 关闭光标
    CLOSE product_list;
    # 返回结果
    RETURN v_product_amount;
END
$$

4.流程控制

# 1.IF语句
IF search_condition THEN statement_list
    [ELSEIF search_condition THEN statement_list] ...
    [ELSE statement_list]
END IF

# 2.CASE语句
CASE case_value
    WHEN when_value THEN statement_list
    [WHEN when_value THEN statement_list] ...
    [ELSE statement_list]
END CASE
# 或
CASE
    WHEN search_condition THEN statement_list
    [WHEN search_condition THEN statement_list] ...
    [ELSE statement_list]
END CASE

# 3.LOOP(循环) + LEAVE(类似break: 退出) + ITERATE(类似continue: 直接进入下一轮循环)语句示例:
outer: LOOP
    set @x = @x + 1;
    IF @x = 100 THEN
        # break
        LEAVE outer;
    ELSE
        # continue
        ITERATE outer;
    END IF;
END LOOP outer;

# 4.REPEAT: 条件满足时退出循环
[label:] REPEAT
    statement_list
UNTIL search_condition
END REPEAT[label]

# 5.WHILE: 条件满足时执行循环
[label:] WHILE search_condition DO
    statement_list
END WHILE[label]

5.事件调度器: 类似Linux下的

crontab

# 创建EVENT
CREATE EVENT uuid_generate_event
    ON SCHEDULE EVERY 10 SECOND
    DO
        INSERT INTO e_mall.uuid_gen(uuid) values (REPLACE(UUID(),'-',''));
# 查看所有EVENT
SHOW EVENTS\G
# 删除EVENT
DROP EVENT uuid_generate_event;

6.触发器

触发器只能创建在永久表(Permanent Table)上, 不能用于临时表(Temporary Table)

# 创建触发器
CREATE TRIGGER trigger_name trigger_time trigger_event
    ON table_name FOR EACH ROW trigger_statement
# trigger_time: 触发时间, 分为BEFORE(检查约束前触发)和AFTER(检查约束后触发)
# trigger_event: 触发事件, INSERT, UPDATE 或 DELETE
DELIMITER $$
CREATE TRIGGER insert_user_trigger
AFTER INSERT ON user FOR EACH ROW
BEGIN
    insert into uuid_gen(uuid) values (REPLACE(UUID(),'-',''));
END
$$
DELIMITER ;

# 查看触发器
show triggers\G
# 删除触发器
drop trigger insert_user_trigger;

六、事务

1.普通事务

start transaction

commit

rollback

commit and chain; (自动开启一个新的事务)

# 开启事务
start transaction;
# 执行SQL
delete from product_order where id = 8;
# 此时查询时id=8的记录已删除
select * from product_order;
# 回滚事务
rollback;
# 回滚后可以查询到id=8的记录
select * from product_order;

2.分布式事务: XA事务

# 1.流程
# 1).启动XA事务
XA {START|BEGIN} xid [JOIN|RESUME]
# xid为XA事务标识符, 格式为 xid: gtrid[, bqual[, formatID]]
# gtrid: 分布式事务标识符, 同一个分布式事务应使用相同的gtrid
# bqual: 分支限定符, 一个分布式事务中的每个分支事务, 其bqual值必须唯一
# formatID: 用于标识gtrid和bqual值使用的格式, 默认值为1
# 2).执行业务SQL
# 3).XA事务完结
XA END xid
# 4).XA分支事务准备
XA PREPARE xid
# 5).XA分支事务详细信息查询(辅助功能)
XA RECOVER
# 6).提交XA分支事务
XA COMMIT xid
# 7).或者回滚分支事务
XA ROLLBACK xid

# 2.示例
# 1).启动一个分支事务, 产品库存减1, xid的gtrid为'order_tran', bqual为'product'
XA START 'order_tran'.'product';
UPDATE product SET stock = stock - 1 where id = 1;
XA END 'order_tran'.'product';
# 2).启动另一个分支事务, 插入订单
XA START 'order_tran'.'order';
INSERT INTO product_order(product_id, create_time) VALUES (1, NOW());
XA END 'order_tran'.'order';
# 3).'product'分支事务准备提交
XA PREPARE 'order_tran'.'product';
# 4).'order'分支事务准备提交
XA PREPARE 'order_tran'.'order';
# 5).提交所有分支事务
XA COMMIT 'order_tran'.'product';
XA COMMIT 'order_tran'.'order';

本篇关于《MySQL基础语法》的介绍就到此结束啦，但是学无止境，想要了解学习更多关于数据库的相关知识，请关注golang学习网公众号！