Detailed explanation of MySQL sql99 syntax inner join and non-equivalent join

#Case: Query employee salary levels

SELECT
  salary,grade_level
FROM
  employees
JOIN
  job_grades g
ON
  e.`salary` BETWEEN g.`lowest_sal` AND g.`lowest_sal`;

#Example: Query the number of each salary level and sort by level in descending order

SELECT
  COUNT(*),grade_level
FROM
  job_grades j
JOIN
  employees
ON
  e.`salary` BETWEEN j.`lowest_sal` AND j.`highest_sal`
GROUP BY
  grade_level DESC;

Content extension :

grammar

select query list

from Table 1 Alias ​​[Connection Type]

jion Table 2 Alias

on connection condition

[where filter conditions]

[group by grouping]

[having filter conditions]

[order by sort list]

Case 1: Query employee name, department name

SELECT last_name,department_name
FROM employees
INNER JOIN departments d
ON e.department_id=d.department_id;

Case 2: Query the employee names and job titles containing "e" (add filter)

SELECT last_name,job_title
FROM employees
INNER JOIN jobs j
ON e.job_id=j.job_id
WHERE e.last_name LIKE '%e%';

The above is all the knowledge points introduced this time.