? ?????? WHERE, HAVING, ORDER BY, GROUP BY ?? SQL ?? ?? ?? ?? ?? ? ?? ???? ?? ??? ?? ?????.
??
- ??? ??
- WHERE ?
- GROUP BY ?
- HAVING ?
- ORDER BY ??
- LIMIT ??
- DISTINCT ??
- AND, OR, NOT ???
??? ??
?? ???
| emp_id | name | age | department_id | hire_date | salary |
|---|---|---|---|---|---|
| 1 | John Smith | 35 | 101 | 2020-01-01 | 5000 |
| 2 | Jane Doe | 28 | 102 | 2019-03-15 | 6000 |
| 3 | Alice Johnson | 40 | 103 | 2018-06-20 | 7000 |
| 4 | Bob Brown | 55 | NULL | 2015-11-10 | 8000 |
| 5 | Charlie Black | 30 | 102 | 2021-02-01 | 5500 |
?? ???
| dept_id | dept_name |
|---|---|
| 101 | HR |
| 102 | IT |
| 103 | Finance |
| 104 | Marketing |
WHERE ?
WHERE ?? ??? ??? ?? ???? ????? ? ?????.
SQL ??
SELECT name, age, salary FROM employees WHERE age > 30;
??
| name | age | salary |
|---|---|---|
| John Smith | 35 | 5000 |
| Alice Johnson | 40 | 7000 |
| Bob Brown | 55 | 8000 |
??: WHERE ?? 30? ??? ??? ????? ?? ??????.
AND ???? ?
SELECT name, age, salary FROM employees WHERE age > 30 AND salary > 5000;
??
| name | age | salary |
|---|---|---|
| Alice Johnson | 40 | 7000 |
| Bob Brown | 55 | 8000 |
??: WHERE ?? 30? ??, ??? 5000 ??? ??? ??????.
GROUP BY ?
GROUP BY ?? ? ??? ?? ?? ?? ?? ?? ??? ?? ?? ?? ?? ??? ????? ? ?????.
SQL ??
SELECT name, age, salary FROM employees WHERE age > 30;
??
| department_id | employee_count |
|---|---|
| 101 | 1 |
| 102 | 2 |
| 103 | 1 |
??: GROUP BY ?? ??? Department_id?? ????? ? ??? ?? ?? ?????.
HAVING ?
HAVING ?? GROUP BY ?? ??? ??? ????? ? ?????. WHERE ?? ???? ????? ?? ?? ?????.
SQL ??
SELECT name, age, salary FROM employees WHERE age > 30 AND salary > 5000;
??
| department_id | avg_salary |
|---|---|
| 102 | 5750 |
| 103 | 7000 |
??: HAVING ?? ? ?? ??? ?? ??? ???? ??? ??????. ????? 5500 ??? ??? ?????.
ORDER BY ??
ORDER BY ?? ?? ??? ?? ???? ?? ??? ???? ? ?????. ????? ?????? ?????. ?????? ????? DESC? ?????.
SQL ??(????)
SELECT department_id, COUNT(*) AS employee_count FROM employees GROUP BY department_id;
??
| name | salary |
|---|---|
| John Smith | 5000 |
| Charlie Black | 5500 |
| Jane Doe | 6000 |
| Alice Johnson | 7000 |
| Bob Brown | 8000 |
??: ?? ?? ?????? ??? ?????.
SQL ??(????)
SELECT department_id, AVG(salary) AS avg_salary FROM employees GROUP BY department_id HAVING AVG(salary) > 5500;
??
| name | salary |
|---|---|
| Bob Brown | 8000 |
| Alice Johnson | 7000 |
| Jane Doe | 6000 |
| Charlie Black | 5500 |
| John Smith | 5000 |
??: ?? ?????? ??? ?????.
LIMIT ??
LIMIT ?? ?? ???? ??? ??? ?? ???? ? ?????. ?? ??? ?? ??? ?????? ???? ? ?? ?????.
SQL ??
SELECT name, age, salary FROM employees WHERE age > 30;
??
| name | salary |
|---|---|
| Bob Brown | 8000 |
| Alice Johnson | 7000 |
| Jane Doe | 6000 |
??: LIMIT ?? ??? ?? ?? ?? ?? 3???? ??? ?????.
DISTINCT ??
DISTINCT ?? ?? ???? ???(??) ?? ???? ??? ???? ? ?????.
SQL ??
SELECT name, age, salary FROM employees WHERE age > 30 AND salary > 5000;
??
| department_id |
|---|
| 101 |
| 102 |
| 103 |
??: DISTINCT ?? ??? ???? ??? Department_id ?? ?????.
AND, OR, NOT ???
AND, OR ? NOT ???? WHERE ??? ?? ??? ???? ? ?????.
AND ???
AND ???? ? ? ??? ??? ???? ? ?????. ???? ?? ??? true? ?? ?????.
SELECT department_id, COUNT(*) AS employee_count FROM employees GROUP BY department_id;
??
| name | age | salary |
|---|---|---|
| Alice Johnson | 40 | 7000 |
| Bob Brown | 55 | 8000 |
??: WHERE ?? ? ??(?? > 30 ? ?? > 5500)? ?? ?? ?? ??????.
OR ???
OR ???? ?? ? ??? ???? ?? ??? ?????.
SELECT department_id, AVG(salary) AS avg_salary FROM employees GROUP BY department_id HAVING AVG(salary) > 5500;
??
| name | age | salary |
|---|---|---|
| Jane Doe | 28 | 6000 |
| Alice Johnson | 40 | 7000 |
| Bob Brown | 55 | 8000 |
??: WHERE ?? age < 30 ?? ?? > 7000? ????.
NOT ???
NOT ???? ??? true? ?? ???? ? ?????.
SELECT name, age, salary FROM employees WHERE age > 30;??
name age salary John Smith 35 5000 Charlie Black 30 5500 Jane Doe 28 6000 ??: WHERE ?? ?? > 6000? ?????. ?, ??? 6000 ??? ??? ????? ?????.
??
? ?????? ?? ? ?? ???? ?? ?? ?? SQL? WHERE, HAVING, ORDER BY, GROUP BY ? ?? ?? ???? ???? ???, ??? ? ???? ??? ?????. ???? SQL ?? ??, ??? ??, ?????? ??? ????? ????? ??? ??? ???? ?? ?????.
? ??? ?? ??? ??? SQL ??? ? ??? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!
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