mysql 多条语句合并查询

select count(*) from matches where StartTime > 1519315200 and endtime < 1519401600 and matchtype = 1 union all
select count(*) from matches where StartTime > 1519315200 and endtime < 1519401600 and matchtype = 2 union all
select count(*) from matches where StartTime > 1519315200 and endtime < 1519401600 and matchtype = 3; 

　　

union不允许重复的值  union all 允许重复值



select distinct name from table  查询去除重复键值

1.查看数据库编码格式

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mysql> show variables like 'character_set_database';
 2.查看数据表的编码格式

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mysql> show create table <表名>;
 3.创建数据库时指定数据库的字符集

mysql>create database <数据库名> character set utf8;
4.创建数据表时指定数据表的编码格式

create table tb_books (
    name varchar(45) not null,
    price double not null,
    bookCount int not null,
    author varchar(45) not null ) default charset = utf8;
5.修改数据库的编码格式

mysql>alter database <数据库名> character set utf8;
6.修改数据表格编码格式

mysql>alter table <表名> character set utf8;
7.修改字段编码格式

mysql>alter table <表名> change <字段名> <字段名> <类型> character set utf8;

mysql>alter table user change username username varchar(20) character set utf8 not null;
 8.添加外键

mysql>alter table tb_product add constraint fk_1 foreign key(factoryid) references tb_factory(factoryid);
mysql>alter table <表名> add constraint <外键名> foreign key<字段名> REFERENCES <外表表名><字段名>;
9.删除外键

mysql>alter table tb_people drop foreign key fk_1;
mysql>alter table <表名> drop foreign key <外键名>;

自动增加列号
select (@i:=@i+1) as ord_num,time from log,(select @i:=0)b limit 10;

增加自定义列和内容
select "0~24" as "时间段",count(1) from log

from_unixtime将时间戳格式化

SELECT DISTINCT userid1 from ningxia_logic.video where from_unixtime(Time) > '2017-03-24 16:40:00' and from_unixtime(Time) < '2017-03-24 18:05:00'

unix_timestamp 将格式化，转成时间戳

yesterDate=`date +%Y%m%d -d -1day`
curDate=`date +%Y%m%d`

unix_timestamp（yesterDate）