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-- View all clients
SELECT * FROM clients;

-- Count how many clients are in the database
SELECT COUNT(*) FROM clients;

-- Count how many clients have provided their email
SELECT COUNT(email) FROM clients;

-- View all clients orders
SELECT * FROM client_orders;

-- Calculate the total order amount across all orders
SELECT SUM(order_total) FROM client_orders;

-- Show both client count and total order value in one query
SELECT COUNT(*) AS total_clients, SUM(order_total) AS total_revenue
FROM client_orders;

# COUNT and SUM

Two of the most useful SQL tools for summarizing data are `COUNT()` and `SUM()`.  
They help you answer questions like:

- How many orders were placed?
- What's the total amount spent?

<br/>

## COUNT: How Many Rows?

`COUNT()` is used to count rows in a table.

```sql title="Count total clients"
SELECT COUNT(*) 
FROM clients;
```

This returns the total number of rows in the `clients` table.

To count only non-null values in a column, you can use the `COUNT()` function with a column name.

```sql title="Count clients with email"
SELECT COUNT(email)
FROM clients;
```

<br/>

## SUM: Add Up Values

`SUM()` adds together values from a numeric column.

```sql title="Total sales"
SELECT SUM(order_total)
FROM client_orders;
```

This returns the total amount spent across all orders.

> **Note:** Works only with numeric types like `INT` or `REAL`.

<br/>

## What's Next?

Next up: learn how to use `AVG()`, `MAX()`, and `MIN()` to measure averages and find highest or lowest values.

`SUM()` is specifically designed to add up numeric values from a column, not to count rows. To count rows, you should use the `COUNT()` function, which is intended for calculating the number of entries in a table or the number of non-null values in a column.

### The SQL function `SUM()` can be used to count the number of rows in a table.

COUNT and SUM

COUNT: How Many Rows?

SUM: Add Up Values

What's Next?

The SQL function SUM() can be used to count the number of rows in a table.

The SQL function `SUM()` can be used to count the number of rows in a table.