Summary  
This chapter explains how to use UPDATE statements to modify existing table records and DELETE statements to remove specific rows using conditional clauses.

General domain of usage  
Pharmaceutical inventory management.

In this video, you will learn how to use the UPDATE and DELETE statements in SQL. See step-by-step demonstrations of how to change existing data in a table with UPDATE, using conditions to target specific rows. Then, watch how the DELETE statement removes rows from a table, and learn why including a WHERE clause is critical to avoid deleting all data. Practical examples with the medications table will help you understand how these commands work in real-world scenarios.

It's time to get back to **writing queries** and consider two more statements.

You already know how to clear a table, add a column, insert data, etc. But for proper interaction with the database, we need to understand **how to update and delete individual rows**. 

For this, there are two statements and types of queries: the `UPDATE` and the `DELETE` queries.

Let's look at an example with the `medications` table:

Let's imagine we need to **update the price for a specific type of medication**. For example, currently, there's a **50%** discount on `ibuprofen`, and we need to change the price for this product. 

Our `UPDATE` query will look like this:

UPDATE medications
SET price = 4
WHERE id = 2;

SELECT * 
FROM medications
ORDER BY id;

Here, we updated the `medications` table so that the `price` for the product with `id` 2 (ibuprofen) will be set to `4`. After that, we **selected all the columns from the table** to ensure the `price` column was successfully updated. You can substitute any value and see how the update operation works in SQL:



```sql
UPDATE table_name
SET column_name = value
WHERE some_condition;
```

The syntax for deletion will look like this:

```sql
DELETE FROM table_name
WHERE some_condition;
```

But I'll remind you that deleting rows should be done with caution, as you won't be able to simply recover them.

>Note
>
>If you don't include a `WHERE` condition, the data will be updated or deleted for all rows.

This course is perfect for those who already have a basic understanding of SQL and want to delve into more advanced concepts to craft more powerful queries. Throughout the course, you will become familiar with data grouping and filtering grouped data. You will also learn how to work with multiple tables simultaneously, including how to combine them. Additionally, you will explore different types of table joins and how to apply them in practice.

In this section, you will learn how to group and manage data effectively. We will introduce the GROUP BY operator for grouping data. Additionally, you will learn how to filter grouped data using the HAVING operator.

You will learn about nested subqueries, how to create them, and how to use them effectively.

Here, you will learn how to combine multiple tables, allowing you to work with a unified table and simplify query creation.

Learn the fundamentals of Data Definition Language (DDL) and Data Manipulation Language (DML) in SQL, including how to create, modify, and delete database objects, as well as how to insert, update, and delete data within tables.

UPDATE and DELETE

Brief Instructions

解答