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The `WHERE` **operator** in SQL is used to **filter rows**, that is, to select only the records satisfying a given condition.

**Syntax:**

```sql
SELECT Column1, Column2, ...
FROM Table_Name
WHERE Condition;
```

### Usage examples

1. **A simple comparison:**

```sql
SELECT * 
FROM Employees
WHERE Age = 30;
```

- Selects only employees whose age is 30.

2. **A range comparison:**

```sql
SELECT * 
FROM Employees
WHERE Age > 25 AND Age < 40;
```

- Selects employees between 26 and 39 years old.

3. **A set-membership check:**

```sql
SELECT * 
FROM Employees
WHERE DepartmentID IN (101, 102);
```

- Selects employees from departments 101 or 102.

4. **Using patterns:**

```sql
SELECT * 
FROM Employees
WHERE Name LIKE 'A%';
```

- Selects employees whose names start with the letter "A".

**Notes:**

- `WHERE` is applied **before grouping (**`GROUP BY`**) and sorting (**`ORDER BY`**)**.
- Conditions can be combined with `AND`, `OR`, `NOT`.

> Put simply, `WHERE` is SQL's tool for **filtering out unneeded rows and selecting only the data you need**.

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