1. Select all/distinct field name/alias from table where condition + [1] + [2] + [3];
where conditions: >, <, ≥, ≤, like, between and (closed interval), in, not in, and &&, or ||, not!
all: query to all
distinct: remove duplicate results
[1]: group by [asc/desc] asc: ascending order, desc: descending order
【2】:order by
[3]: limit limit 3: Take the first 3 records; limit 2,3: Starting from the third record, take a total of 3 records (starting from position 2, length is 3)
1. Demonstration by example
First build a table, id is the primary key (primary key), and auto-increment (auto_increment)
create table testabc (id int primary key auto_increment,name varchar(4));
adding data
insert into testabc set name='a';
Bulk add
insert into testabc (name) values ('a'),('b'),('c'),('c'),('a'),('a');
select * from testabc where name='a';
select * from testabc group by name;
Limit the first 3 select * from testabc limit 3;
select * from testabc limit 2,3; starting from the third record, take a total of 3 records (starting from position 2, length is 3)
2. Commonly used functions max(), min(), avg(), count(), count()---When the record value is NULL, the number of entries is not counted
1. For example, the table is as follows
select max(age) from stu;
select sex, count(*) from stu group by sex;
select sex,count(*),max(age),avg(age) from stu group by sex;
