# COALESCE

The `COALESCE` function in SQL is used to manage NULL values in data. It scans from left to right through the arguments and returns the first argument that is not `NULL`.

Syntax: 
```sql
COALESCE(value1,value2,..., valueN)
```
The `COALESCE` function allows handling the case where you have possible `NULL` values in your data and you want to replace it with some other value.

For instance, here is an example of how you might use `COALESCE`:

```sql
SELECT product_name, COALESCE(price, 0) AS Price 
FROM products;
```
In this example, if the "price" column for a product entry is `NULL`, it will instead return "0".

Another common use case is using `COALESCE` to find the first non-NULL value in a list:

```sql
SELECT COALESCE(NULL, NULL, 'third value', 'fourth value');
```
In this case, it would return "third value", as that's the first non-NULL value in the list.

Remember, `COALESCE` does not update the original data. It only returns the first non-NULL value in the runtime. To update any NULL values permanently, you would need to use an `UPDATE` statement. 

The `COALESCE` function in SQL improves the reliability of your queries when null values are involved. Whether it's replacing nulls with default values or finding the earliest valid date, it's a very useful function to grasp.