Summary  
This chapter explains how to implement code for updating and deleting specific rows in a relational database using SQL’s UPDATE and DELETE statements, showing how to change column values conditionally and remove records with care.

General domain of usage  
Relational database management

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.

`UPDATE`: Used to modify existing data in a table. With this type of query, we can change data in a table without affecting other rows.

Definition

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 operation of the `DELETE` statement is almost identical in principle. However, here we do not use the keyword `SET` because we are not changing anything; we are simply deleting rows.

The syntax for deletion will look like this:

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

Deleting rows should be done with caution, as you won't be able to simply recover them.

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

Note

Dette kursus er perfekt for dem, der allerede har en grundlæggende forståelse af SQL og ønsker at dykke ned i mere avancerede begreber for at skabe mere kraftfulde forespørgsler. Gennem kurset vil du blive fortrolig med datagruppering og filtrering af grupperede data. Du vil også lære at arbejde med flere tabeller samtidigt, herunder hvordan man kombinerer dem. Derudover vil du udforske forskellige typer tabelsammenføjninger og hvordan man anvender dem i praksis.

I dette afsnit lærer du, hvordan du effektivt grupperer og håndterer data. Vi introducerer GROUP BY-operatoren til gruppering af data. Derudover lærer du, hvordan du filtrerer grupperede data ved hjælp af HAVING-operatoren.

Du vil lære om indlejrede underforespørgsler, hvordan de oprettes, og hvordan de anvendes effektivt.

Her lærer du, hvordan du kombinerer flere tabeller, hvilket gør det muligt at arbejde med en samlet tabel og forenkle oprettelsen af forespørgsler.

Lær grundlæggende om Data Definition Language (DDL) og Data Manipulation Language (DML) i SQL, herunder hvordan man opretter, ændrer og sletter databaseobjekter, samt hvordan man indsætter, opdaterer og sletter data i tabeller.

UPDATE and DELETE

Brief Instructions

Løsning