DQL

SELECT *FROM BB;基础查询语句
插入字段可以不传值的情况：
1、自增的字段可以不传值；
2、有默认值；
3、可为空的字段可以不传值；

指定字段查询：
select name,age,sex from bb;
select province from bb;
select distinct province from bb;把重复的去掉
select name from bb where age > 56;查询年龄大于56的人名是什么
select *from bb where age > 34;
select name from bb where age > and money =4000;
select *from bb where age between 1 and 5; 包括1和5；在闭区间年龄是1和5内的数据
between and 闭区间
in/not in 在/不在指定的集合内
select *from bb where age in(1,3,5,7);年龄是1,3,5,7的数据
select *from bb where age not in(1,3,5,7);年龄是1,3,5,7的数据
like 模糊查询
select *from bb where name like  '_玲'；把两个字中第二个字是玲的查询出来，其中_代表任意一个字符
select *from bb where name like '%玲'；只要最后一个字是“玲”就行，不管”玲“前面几个字。%代表：匹配“玲”前面所有字符；
select *from bb where name like '林%';查询只要是“林”开头的就行,不管“林”后面几个字
排序：
select *from bb order by money;默认是从低到高排序；
select *from bb order by money desc;  desc： 降序
多字段排序
select *from bb order by money desc,age desc;如果金钱相等，就按照年龄降序排序；
asc:升序
多字段排序用逗号隔开
limit：限制，limit 偏移量，数量；
limit 2,3;从第二个开始显示3个数据；
limit 0,3;
select *from bb order by money desc limit 3;只显示前三个

select max(money) from bb;
min()
avg()平均
count()多少个
sum()总数
max()

分组

select province,count(province) from bb group by province;根据省份分组显示省份和省份的个数；
可以起别名:as 可以省略
select province as pro,count(province) as count from bb group by province;
having:对结果进行限制，where对表限制，having对组限制
select province as pro,count(province) as count from bb group by province having count > 2;
select province as pro,count(province) as count from bb group by province having count > 2 order by desc limit 1,1;

implode(join)将一个数组按照什么进行分割
explode把一个字符串分割成数组