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? ??? ??? MySQL ???? MySQL ? ?????: ?? ??? ? ???? ?? ?? ???

MySQL ? ?????: ?? ??? ? ???? ?? ?? ???

Dec 23, 2024 am 05:01 AM

Mastering MySQL Views: A Comprehensive Guide to Query Abstraction and Optimization

MySQL ? ?????: ?? ???? ? ????

MySQL ?? ??? ??? ????? ?? ???? ???? ??? ???? ??? ? ?? ??? ?????. ?? ???? ??? ????? SQL ??? ? ???? ?? ???? ?? ??? ? ??? ???. ??? ?? ??? ????? ??? ?? ??? ???? ??? ????. ? ???? MySQL ? ??? ??, ?? ? ?? ??? ?????.

MySQL ?? ??????

MySQL? ?? ????? ?? ??????. ?? ???? ??? ??? ? ?? ??? SELECT ?????. ???? ? ??? ???? ?? ?? ??? ??? ???? ?????.

CREATE VIEW active_employees AS
SELECT id, name, department
FROM employees
WHERE status = 'active';

??? active_employees? ?? ?? ?? ??? ?? ??? ???? ????. ?? ????? active_employees? ??? ? ????.

SELECT * FROM active_employees;

? ??? ??

  1. ???? ??: ???? ??? JOIN, ?? ?? ? ??? ??? ???? ??? ??? ??? ????? ??? ???? ????. 
   -- Without a view
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- With a view
   CREATE VIEW new_york_employees AS
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- Querying the view
   SELECT * FROM new_york_employees;

  1. ??? ???: ?? ?????? ???? ???? ???? ?? ? ???? ???? ???? ? ?? ?? ??? ? ????.

  2. ?? ????: ?? ???? ?? ???? ?? ???? ? ???? ??? ???? DRY(Don't Repeat Yourself) ??? ?????.

  3. ??: ?? ???? ?? ??? ?? ????? ???? ??? ??? ?????.

   CREATE VIEW restricted_employee_data AS
   SELECT name, department
   FROM employees
   WHERE access_level = 'limited';

? ?? ?? ??? ??? ???? ??? ?? ?? ? ? ??? ??, ???? ? ??? ???? ? ? ????.

?? ?? ??

?? ?? ??? ????? ?? ?? ???? ??? ?? ??? ??? ?? ????. ?? ????? ????(???? ???? ??? ?? ??? ???). ??? ?? ???? ?? ?? ??? ????? ?? ???? ?? ?? ??? ??? ? ????.

???? ?? ??:

  1. ?? ??? ??: ?? ?? ?? ???? ?? ?? ??? JOIN ?? ?? ??? ?? ?? ???.
  2. ?? ?? ?: ?? ?(?? ?? ?)? ???? ?? ??? ??? MySQL? ? ?? ?? ?? ??? ???? ??? ??? ??? ? ????.
  3. ? ??? ??: MySQL ??? ???? ???? ????? ?? ??? ???? ???? ? ??? ??? ?? ? ????.

? ?? ???? ?? ?? ??:

  • ??? ? ??: ?? ??? ???? ?????. ????? ??? ?? ??? ?? ?? ??? ??? ?? ?? ?? ??? ????.
  • ?? ???? ??????? ??: ?? ??? ?? ? ??? ???? ???? ??? ?? ? ???? ?? ???? JOIN ? WHERE ?? ???? ??? ??????? ?????.
  • ??? ??? ? ? ??: ??? ?? ?? ???? ?? ?? ?? ?? JOIN ?? ?? ??? ???(CTE)?? ??? ?? ? ???? ? ????.

MySQL?? ?? ???? ???? ??

1. ? ??

?? ????? CREATE VIEW ? ??? SELECT ??? ?????. ?? SELECT ??? ??? ???? ?? ???? ???.

CREATE VIEW active_employees AS
SELECT id, name, department
FROM employees
WHERE status = 'active';

2. ? ??

?? ???? ?? ????? ??? ? ????.

SELECT * FROM active_employees;

3. ? ????

?? ?? ??? ???? ?? ?? CREATE OR REPLACE VIEW ?? ???? ? ??? ????? ? ????.

   -- Without a view
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- With a view
   CREATE VIEW new_york_employees AS
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- Querying the view
   SELECT * FROM new_york_employees;

4. ??? ??

?? ? ?? ???? ??? DROP VIEW ?? ???? ??? ? ????.

CREATE VIEW active_employees AS
SELECT id, name, department
FROM employees
WHERE status = 'active';

5. ?? ??

  • ??? ??: ?? ???? ?? ? ????. ?? ???? ???? ???? ???.
  • ???? ??? ? ??: ?? ???? ???? ????. ?? ??? ?????.
  • ??? ??? ??: ?? ???? ??? ?? ??? ????? ?? ???? ????? ??? ??? ?? ??? ?? ?? ??? ??? ? ????.

?? ??? ?? ??

  1. ??? ? ?? ?? ?? ?? ??? ???? ???? ??? ??? ? ??? ????? ? ?? ??? ? ????. 
SELECT * FROM active_employees;
  1. ??? ?? ??? ?? ?? ?? ???? ???? ?? ?? ???? ???? ? ?????. 
   -- Without a view
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- With a view
   CREATE VIEW new_york_employees AS
   SELECT employees.name, departments.name
   FROM employees
   JOIN departments ON employees.department_id = departments.id
   WHERE departments.location = 'New York';

   -- Querying the view
   SELECT * FROM new_york_employees;
  1. ??? ??? ?? ? ?? ??? ???? ??? ???? ?? ??? ????? ??? ??? ??? ??? ?? ??? ? ????. 
   CREATE VIEW restricted_employee_data AS
   SELECT name, department
   FROM employees
   WHERE access_level = 'limited';

??

MySQL ??? ?????? ??? ???, ?? ??? ? ??? ?? ???? ? ????. ??? ??? ??????? ?? ???? ???? ???? SQL ??? ???? ? ????. ??? ?? ?? ??? ??? ??????? ?? ? ???? ???? ???. ?? ??? ?????? ??? ?? ????? ??? ??? ??? ???? ?? ??? ????? ???????. ??? ??? ??? ?? MySQL ??? ?????? ?? ? ???? ?? ??? ??? ? ? ????.

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