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-- View all clients
SELECT *
FROM clients;

-- Group by region to see total sales
SELECT region, SUM(sales) AS total_sales
FROM clients
GROUP BY region;

-- Keep only regions with total sales over 25000
SELECT region, SUM(sales) AS total_sales
FROM clients
GROUP BY region
HAVING SUM(sales) > 25000;

-- Show average sales per region
SELECT region, AVG(sales) AS avg_sales
FROM clients
GROUP BY region;

-- Keep only regions with average sales at least 6000
SELECT region, AVG(sales) AS avg_sales
FROM clients
GROUP BY region
HAVING AVG(sales) >= 6000;

-- Combine conditions:
-- total sales over 25000 AND average sales at least 6000
SELECT region,
       SUM(sales) AS total_sales,
       AVG(sales) AS avg_sales
FROM clients
GROUP BY region
HAVING SUM(sales) > 25000
   AND AVG(sales) >= 6000;

# HAVING Clause

The `HAVING` clause lets you **filter groups** after applying aggregation.

It works like `WHERE`, but is used specifically with results that come from `GROUP BY`.

<br/>

## Why Not Use WHERE?

The difference between `WHERE` and `HAVING` is that:

- `WHERE` filters **rows before grouping**
- `HAVING` filters **groups after aggregation**

For example, if you want to find regions with an average sales above a certain amount, you must first group the data and then use HAVING to filter the grouped results.

<br/>

## Basic Syntax

The `HAVING` clause is used after the `GROUP BY` clause in a `SELECT` statement.

```sql title="HAVING Syntax"
SELECT column, AGG_FUNCTION(column)
FROM table_name
GROUP BY column
HAVING condition;
```

<br/>

## Example: Regions with High Sales

Assume you have a table called `clients` and you want to find regions with total sales above 25000.

You can use the `HAVING` clause to filter the results after the data is grouped.

```sql title="Regions with high sales"
SELECT region, SUM(sales) AS total_sales
FROM clients
GROUP BY region
HAVING SUM(sales) > 25000;
```

The HAVING clause is used to filter groups after aggregation, not individual rows before they are grouped. In contrast, the WHERE clause is used to filter rows before any grouping is applied. This distinction is crucial when dealing with SQL queries that involve groupings and aggregations.

### The HAVING clause in SQL is used to filter rows before they are grouped.