100?? ?? ??? ??? SQL ?????

SQL(Structured Query Language)? ?????? ?? ? ??? ?????. ? ?????? ?????? ??? ???? ? ??? ??? ??? ??? ?? 100?? ????? ???? SQL ??? ?????.

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1. ?? SQL ?? ??

1. ????? ?? ???? ???? ??? ?????.

   SELECT * FROM table_name;

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

1. ????? ? ??? ?? ??? ?? ??? ?????.

   SELECT MAX(salary) AS second_highest_salary  
   FROM employees  
   WHERE salary < (SELECT MAX(salary) FROM employees);

1. ??? 'A'? ???? ??? ???? ??? ?????.

   SELECT * FROM employees WHERE name LIKE 'A%';

1. ???? ???? ? ??? ???? ??? ?????.

   SELECT region, SUM(sales) AS total_sales  
   FROM sales_data  
   GROUP BY region;

1. ?? ?? NULL? ?? ???? ???? ??? ?????.

   SELECT * FROM table_name WHERE column_name IS NULL;

1. ????? ?? ?? ???? ??? ?????.

   DELETE FROM table_name  
   WHERE id NOT IN (SELECT MIN(id) FROM table_name GROUP BY column_name);

1. ??? ?????? ???? ??? ?????.

   SELECT * FROM table_name ORDER BY column_name DESC;

1. ???? ? ?? ???? ??? ?????.

   SELECT COUNT(*) FROM table_name;

1. ? ???? ???? ??? ?????.

   SELECT employees.name, departments.department_name  
   FROM employees  
   JOIN departments  
   ON employees.department_id = departments.id;

1. ????? ?? ? ?? ???? ??? ?????.
   

   SELECT * FROM table_name LIMIT 3;
   

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2. SQL ?? ??

1. ?? ???? ??????
   
   ?? ????? ?? ??? ???? ????? ?? ??? ???? ??? ?????.

2. SQL ??? ??? ??? ??? ? ????

   • ??? ?????.
   • SELECT *? ????.
   • ??? ??????.
   • ??? ??? ??? ?????.
   • ????? ?????.

3. ???? ??? ??????
   
   ???? ?????? ???? ??? ?? ?? ??? ??????.

4. ???? ??? ??????

   • ?? ?? ??? ??????.
   • INSERT ? DELETE? ?? ?? ??? ?? ??.

5. ?? ?? ??? ??? ??????
   
   ?? ??? ??? EXPLAIN ???? ?????.
   

   EXPLAIN SELECT * FROM table_name;
   

6. ?? ???? ??????
   
   ?? ??? ???? ?? ?? ??? ???? ?? ??? ?????.

7. ??????? ???? ??????
   
   ??? ??????? ???? ?? ? ??, ???, ???? ?? ???? ????.

8. ?? ??? ?? ??? ???? ?????.

   • ??? ??? ? ?? ???? ???? ?? ? ?? ???? ?????.
   • ??? ??? ?? ??? ???(CPU, RAM)? ?????.

9. ????? ?????? ??? ??? ??? ????
   
   ????? ? ???? ? ?? ???? ?? ???? ??? ?? ??? ??????.

10. ?????? ??? ??????
    
    ???? ???? ???? ?? ?? ??? ?? ?????? ???? ???? ?? ???? ??? ?????.

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3. SQL ?? ??

1. SQL? ?? ??? ??????
   
   ?? ??? SUM, AVG, COUNT ? ?? ??? ?? ?? ??? ?????.

2. COUNT, SUM, AVG? ???? ?????.

   • COUNT: ? ?? ?????.
   • SUM: ?? ?? ????.
   • AVG: ??? ?????.

3. SQL?? ROUND ??? ??? ??????
   

      SELECT * FROM table_name;
   

4. LENGTH ??? ?? ??? ??????
   
   ???? ?? ?? ?????.
   

      SELECT MAX(salary) AS second_highest_salary  
      FROM employees  
      WHERE salary < (SELECT MAX(salary) FROM employees);
   

5. SQL?? CASE?? ???? ?????.
   

      SELECT * FROM employees WHERE name LIKE 'A%';
   

6. COALESCE? ISNULL? ???? ??????

   • COALESCE: ???? null? ?? ? ?? ?? ?????.
   • ISNULL: null?? ???? ??? ??? ????.

7. UPPER, LOWER ?? ??? ??? ??? ??????
   

      SELECT region, SUM(sales) AS total_sales  
      FROM sales_data  
      GROUP BY region;
   

8. NOW() ??? ??? ??????
   
   ?? ??? ??? ?????:
   

      SELECT * FROM table_name WHERE column_name IS NULL;
   

9. CONCAT ??? ???? ??????.
   

      DELETE FROM table_name  
      WHERE id NOT IN (SELECT MIN(id) FROM table_name GROUP BY column_name);
   

10. TRUNCATE? DELETE? ???? ??????

    • TRUNCATE: ?? ? ??? ???? ?? ????? ?? ?? ?????.
    • DELETE: ??? ?? ?? ???? ? ??? ?????.

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?????. ?? Abhay Singh Kathayat???!
?? ?????? ??? ?? ??? ?? ?? ??? ?? ??? ??????. ?? ????? ?? ???? ??? ???? ??????? ???? ?? ??? ????? ??? ?????? ???? ?????.
? ???? ???(kaashshorts28@gmail.com)? ???? ?????.

? ??? ?? ???? ????? ? ?? SQL ??? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!