# Aggregation and ordering operators

#### ORDER BY

The ORDER BY keyword is used to sort the result-set in ascending or descending order.

The ORDER BY keyword sorts the records in ascending order by default. To sort the records in descending order, use the DESC keyword.

```sql
SELECT column1, column2, ... 
FROM table_name 
ORDER BY column1, column2, ... ASC|DESC;
```

#### MIN 

The `MIN()` function returns the smallest value of the selected column.

```sql
SELECT MIN(column_name)
FROM table_name
WHERE condition;
```

#### MAX

The `MAX()` function returns the largest value of the selected column.

```sql
SELECT MAX(column_name)
FROM table_name
WHERE condition;
```

#### COUNT

The `COUNT()` function returns the number of rows that matches a specified criterion.

```sql
SELECT COUNT(column_name)
FROM table_name
WHERE condition;

```

#### AVG

The AVG() function returns the average value of a numeric column.

```sql
SELECT AVG(column_name)
FROM table_name
WHERE condition;
```

#### SUM

The SUM() function returns the total sum of a numeric column.

```sql
SELECT SUM(column_name)
FROM table_name
WHERE condition;
```

#### GROUP BY

The `GROUP BY` statement groups rows that have the same values into summary rows, like "find the number of customers in each country".

The `GROUP BY` statement is often used with aggregate functions (`COUNT()`, `MAX()`, `MIN()`, `SUM()`, `AVG()`) to group the result-set by one or more columns.

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

#### HAVING

The `HAVING` clause was added to SQL because the `WHERE` keyword cannot be used with aggregate functions.

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

#### References

* <https://www.sqltutorial.org/sql-aggregate-functions/>
* <https://www.w3schools.com/sql/sql_min_max.asp>
* <https://www.w3schools.com/sql/sql_count_avg_sum.asp>
* <https://www.w3schools.com/sql/sql_groupby.asp>