SQL DELETE Statement

SQL DELETE Statement क्या है?

SQL DELETE Statement का उपयोग database table से existing records (rows) को remove करने के लिए किया जाता है। जब किसी data की अब जरूरत न हो या वह गलत हो, तब DELETE statement का इस्तेमाल किया जाता है।

Simple भाषा में
DELETE = table से data हटाना

DELETE Statement का Basic Syntax

DELETE FROM table_name
WHERE condition;

यहाँ:

• table_name → जिस table से data delete करना है
• WHERE → किन records को delete करना है

Example Table

मान लीजिए हमारे पास students नाम की table है:

id	name	age	city
1	Rahul	21	Delhi
2	Aman	23	Jaipur
3	Neha	21	Mumbai
4	Rohit	19	Delhi

Example 1: Single Record Delete करना

अगर हमें Aman का record delete करना है:

DELETE FROM students
WHERE id = 2;

इस query के execute होते ही id = 2 वाला record table से हट जाएगा।

Example 2: Multiple Records Delete करना

DELETE FROM students
WHERE city = 'Delhi';

यह query Delhi city वाले सभी students के records delete कर देगी।

DELETE with AND Operator

DELETE FROM students
WHERE age > 20 AND city = 'Mumbai';

DELETE with OR Operator

DELETE FROM students
WHERE age < 20 OR city = 'Jaipur';

DELETE with IN Operator

DELETE FROM students
WHERE city IN ('Delhi', 'Mumbai');

DELETE with LIKE Operator

DELETE FROM students
WHERE name LIKE 'R%';

DELETE with NULL Condition

DELETE FROM students
WHERE city IS NULL;

DELETE Without WHERE

अगर DELETE statement में WHERE clause नहीं लगाया गया, तो पूरी table खाली हो जाएगी।

DELETE FROM students;

Table structure रहेगा, लेकिन सभी rows delete हो जाएँगी।

DELETE vs TRUNCATE

DELETE	TRUNCATE
WHERE clause supported	WHERE clause नहीं
Row by row delete	पूरी table एक साथ clear
Rollback possible	Rollback नहीं
Slow होता है	Fast होता है

DELETE with Subquery

DELETE FROM students
WHERE id IN (
  SELECT id
  FROM students
  WHERE age > 22
);

Safety Tips

• DELETE से पहले SELECT चला कर data check करें
• Important data के लिए WHERE जरूर लगाएँ
• Production database में सावधानी रखें

Example:

SELECT * FROM students
WHERE city = 'Delhi';

फिर DELETE करें।

Common Mistakes

• WHERE clause भूल जाना
• Wrong condition लगाना
• Backup न लेना

Incorrect example:

DELETE students;

Correct example:

DELETE FROM students;

Summary

• DELETE statement records हटाने के लिए उपयोग होता है
• WHERE clause बहुत important है
• Multiple conditions के साथ delete किया जा सकता है
• TRUNCATE से अलग होता है