DQL数据查询语言

--查询全表
select * from t_hq_ryxx;

--查询字段
select xingm as 姓名 ,gongz as 工资 from t_hq_ryxx;

--链接字段查询
select xingm || xingb as 姓名性别 from t_hq_ryxx

--去除重复查询
select distinct bumbm from t_hq_ryxx;

--排序查询 desc 降序 asc升序
select * from t_hq_ryxx order by bumbm desc;

--组合排序查询 nulls first 空值排序在前 nulls last 空值排序在后
select bumbm as 部门编码,t.* from t_hq_ryxx t order by xingb desc，bumbm

nulls first;

--数字代表字段列表序号
select * from t_hq_ryxx order by 4;

--组合、表达式排序查询
select * from t_hq_ryxx order by xingm || xingb;

--where条件查询
select * from t_hq_ryxx where xingb = 1 and bumbm = 103;

select * from t_hq_ryxx where bumbm is not null;

select * from t_hq_ryxx where bumbm in (103,104,106);

select * from t_hq_ryxx where gongz between 3000 and 4000;

--模糊查询 % 任意位数通配符 _ 一位通配符
select * from t_hq_ryxx where xingm like '%s%'

select * from t_hq_ryxx where xingm like 'a_d'

--子查询
select * from t_hq_ryxx where bumbm in (select bumbm from t_hq_bm where dianh

= '10086');

--分组查询 group by 配合 having使用，进行过滤
select bumbm,count(1) as 数量 , avg(gongz) as 平均工资 from t_hq_ryxx group by bumbm having avg（gongz）> 4000;