The following query selects names of all employees who have been given a bonus (i.e., Bonus is not null) and works in the department D01.

Question

Accepted Answer

> [!TLDR]
> The query uses `WHERE` with two conditions — `Bonus IS NOT NULL` and `DeptId = 'D01'` — connected by `AND`. On the real EMPLOYEE table (Table 9.8) this returns **Kritika** and **Shabbir**.

## The real EMPLOYEE table (Table 9.8)

| EmpNo | Ename | Salary | Bonus | DeptId |
|---|---|---|---|---|
| 101 | Aaliya | 10000 | 234 | D02 |
| 102 | Kritika | 60000 | 123 | D01 |
| 103 | Shabbir | 45000 | 566 | D01 |
| 104 | Gurpreet | 19000 | 565 | D04 |
| 105 | Joseph | 34000 | 875 | D03 |
| 106 | Sanya | 48000 | 695 | D02 |
| 107 | Vergese | 15000 | NULL | D01 |
| 108 | Nachaobi | 29000 | NULL | D05 |
| 109 | Daribha | 42000 | NULL | D04 |
| 110 | Tanya | 50000 | 467 | D05 |

The core idea here is **filtering with multiple conditions**. SQL's `WHERE` clause lets you specify which rows to keep; when every condition must be true at once, you combine them with `AND`.

For "Bonus is not null", remember `NULL` is not a value — it's the absence of one, so you cannot use `= NULL` or `!= NULL`. SQL provides the special operators `IS NULL` and `IS NOT NULL`.

> [!WARNING]
> A common mistake is writing `Bonus != NULL` or `Bonus = NULL`. Neither works in SQL because `NULL` comparisons always yield unknown, not true or false. Always use `IS NULL` or `IS NOT NULL`.

```sql
mysql> SELECT EName FROM EMPLOYEE
    -> WHERE Bonus IS NOT NULL
    -> AND DeptId = 'D01';
```

**Key lines explained:**
- `SELECT EName` — we only need the employee names, not other columns.
- `FROM EMPLOYEE` — the chapter's own EMPLOYEE table (Table 9.8). …

Q.The following query selects names of all employees who have been given a bonus (i.e., Bonus is not null) and works in the department D01.

Concept understanding — Set Difference

The real EMPLOYEE table (Table 9.8)

EmpNo	Ename	Salary	Bonus	DeptId
101	Aaliya	10000	234	D02
102	Kritika	60000	123	D01
103	Shabbir	45000	566	D01
104	Gurpreet	19000	565	D04
105	Joseph	34000	875	D03
106	Sanya	48000	695	D02
107	Vergese	15000	NULL	D01
108	Nachaobi	29000	NULL	D05
109	Daribha	42000	NULL	D04
110	Tanya	50000	467	D05

Q.The following query selects names of all employees who have been given a bonus (i.e., Bonus is not null) and works in the department D01.

The real EMPLOYEE table (Table 9.8)

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