Create

drop table if exists table_a;
create table table_a as

Select

select a from table where a like %str%: return records that contains str, for example, xxxstryyy
select a from table where a (not) like str%: return records that start with str, for example, strxxxyyy
select a from table where a is null: a is null, otherwise, a is not null
select a from table where a in (a1, a2, a3)

select count(dept_no) from dept_emp group by dept_no order by count(dept_no) desc
select count(dept_no) from dept_emp group by dept_no having count(dept_no) > 5

show tables in db_name

select e.name, s.salary
from employee e
join salaries s
on e.emp_id = s.emp_id