# `HAVING` Clause

Unlike where clause which imposes conditions on columns `Having` clause enables you to specify conditions that filter which group results appear in the results.

## Syntax

```sql
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
HAVING condition
ORDER BY column_name(s);
```

## Description

- Used with `aggregate functions`
- Must follow `GROUP BY` clause in the query

## Aggregate Functions
 - SQL aggregation is the task of collecting a set of values to return a single value.
 - An aggregate function is a function where the values of multiple rows are grouped together as input on certain criteria to form a single value of more significant meaning.
    
## Aggregate Functions Examples

Suppose this are the table given to us

|Students | table||
|--------|-----------|--------|
| rollno | name      | class |
|      1 | Sanskriti | TE    |
|      1 | Shree     | BE    |
|      2 | Harry     | TE    |
|      3 | John      | TE    |
|      3 | Shivani   | TE    |


|purchase | table||
|------------|-------|---------------|
| item       | price | customer_name |
| Pen          |    10 | Sanskriti     |
| Bag          |  1000 | Sanskriti     |
| Vegetables   |   500 | Sanskriti     |
| Shoes        |  5000 | Sanskriti     |
| Water Bottle |   800 | XYZ           |
| Mouse        |   120 | ABC           |
| Sun Glasses  |  1350 | ABC           |


### AVG function 
  
  Calculates `average` of the given column of values

```sql
SELECT AVG(price) AS Avg_Purchase, customer_name
FROM purchase
GROUP BY customer_name;
```

| Avg_Purchase | customer_name |
|--------------|---------------|
|    1627.5000 | Sanskriti     |

### SUM function
  
   Calculates `sum` of values of given column.

```sql
SELECT SUM(price) AS Total_Bill, customer_name
FROM purchase
GROUP BY customer_name;
```

| Total_Bill | customer_name |
|------------|---------------|
|       6510 | Sanskriti     |

### COUNT function 

  Gives `count` of entries/ values in given column.

```sql
SELECT COUNT(item) AS Total_Items, customer_name
FROM purchase
GROUP BY customer_name;
```

| Total_Items | customer_name |
|-------------|---------------|
|           4 | Sanskriti     |

### MAX function

  Return `maximum` value from the number of values in the column.

```sql
SELECT MAX(price) AS Highest_Purchase, customer_name
FROM purchase
GROUP BY customer_name;
```

| Highest_Purchase | customer_name |
|-----------------|---------------|
|             5000 | Sanskriti     |

### MIN function
  
   Return `minimum` value from the number of values in the column.

```sql
SELECT MIN(price) AS Lowest_Purchase, customer_name
FROM purchase
GROUP BY customer_name;
```
| Lowest_Purchase | customer_name |
|-----------------|---------------|
|              10 | Sanskriti     |


## Having clause Examples

### Example 1

```sql
SELECT COUNT(class) AS strength, class
FROM Students
GROUP BY class
HAVING COUNT(class) > 2;
```

Above query gives number of students in a class `having` number of students > 2 

| strength | class |
|----------|-------|
|        4 | TE  |

### Example 2

```sql
SELECT customer_name, MIN(price) AS MIN_PURCHASE
FROM purchase
GROUP BY customer_name
HAVING MIN(price) > 10;
```
Above query finds `minimum` price which is > 10

| customer_name | MIN_PURCHASE |
|---------------|------------|
| XYZ           |        800 |
| ABC           |        120 |

### Example 3

```sql
SELECT customer_name, AVG(price) AS Average_Purchase
FROM purchase
GROUP BY customer_name
HAVING AVG(price) > 550
ORDER BY customer_name DESC;
```
Above query calculates `average` of price and prints customer name and average price which is greater than 550 with descending `order` of customer names.

| customer_name | Average_Purchase |
|---------------|------------------|
| XYZ           |         800.0000 |
| Sanskriti     |        1627.5000 |
| ABC           |         735.0000 |

### Example 4

```sql
SELECT customer_name, SUM(price) AS Total_Purchase
FROM purchase
WHERE customer_name
LIKE "S%"
GROUP BY customer_name
HAVING SUM(price) > 1000;
```
Calculates `SUM` of price and returns customer name and sum > 1000.

| customer_name | Total_Purchase |
|---------------|----------------|
| Sanskriti     |           6510 |