Day 4: SQL

Filtering Data Using WHERE Clause & Operators

1. What is WHERE Clause?
The WHERE clause is used to filter rows that meet a specific condition.
Without it, SELECT returns all rows.
Syntax:
SELECT column1, column2
FROM table_name
WHERE condition;

2. Comparison Operators
Used to compare values.

Operator	Description	Example
=	Equal to	salary = 35000
!= or <>	Not equal	age <> 25
>	Greater than	salary > 30000
<	Less than	age < 30
>=	Greater or equal	salary >= 40000
<=	Less or equal	age <= 22

Example:
SELECT * FROM employees
WHERE salary > 35000;

3. Logical Operators
Combine multiple conditions.
| Operator | Description | Example |
| -------- | -------------------- | -------------------------------------- |
| AND | Both conditions true | salary > 35000 AND department = 'IT' |
| OR | Any condition true | department = 'IT' OR department = 'HR' |
| NOT | Negates condition | NOT department = 'HR' |

Example:
SELECT * FROM employees
WHERE department = 'IT' AND salary > 35000;

4. Pattern Matching with LIKE
Search for patterns in text columns.

Pattern	Description
%	Any number of characters
_	Single character

Examples:
-- Names starting with 'R'
SELECT * FROM employees
WHERE emp_name LIKE 'R%';
-- Names ending with 'a'
SELECT * FROM employees
WHERE emp_name LIKE '%a';
-- Names with 4 letters
SELECT * FROM employees
WHERE emp_name LIKE '____';

5. Filtering with BETWEEN
Select values within a range.
SELECT * FROM employees
WHERE salary BETWEEN 35000 AND 42000;

6. Filtering with IN
Select values from a list.
SELECT * FROM employees
WHERE department IN ('IT', 'HR');

7. Filtering with IS NULL / IS NOT NULL
Check for missing values.
SELECT * FROM employees
WHERE department IS NULL;
SELECT * FROM employees
WHERE department IS NOT NULL;

Comments

[Vigneshwaralingam]

what motivate u to write daily blogs ,and what u gained from writing blogs daily ?and how did u achieve this consistency?