# UPDATE

The `UPDATE` statement modifies existing data within a database table. Utilize this for atomic data changes based on specified criteria,  ensuring data accuracy in application workflows.

Update syntax:

```sql
UPDATE users SET username='software shinobi' WHERE id=1;
```

## Syntax breakdown:

*   `UPDATE users`: Identifies the target table (`users`) for  the modification.
*   `SET username='software shinobi'`: Specifies the column (`username`) to update and its new value.
*   `WHERE id=1`: Filters which rows are affected. Only the row where `id` equals  `1` will be updated.

**Critical Impact:** Omitting the `WHERE` clause updates *every* row in the table. This operation is destructive; confirm intent before executing an `UPDATE` without a filter.

## Update Multiple Rows

Consider a `users` table state  prior to updates:

| id  | username      | about |
| :-- | :------------ | :---- |
| 2   | shinobi       | NULL  |
| 3   | java team six | NULL  |
| 4   | tony          | NULL  |
| 5   | shinobi       | NULL  |
| 6   | java team six | NULL  |
| 7   | tony          | NULL  |

Update all rows in the `about` column:

```sql
UPDATE users SET about='404 bio not found';
```

This query affects all six rows:

```
Query OK, 6 rows affected (0 .02 sec)
Rows matched: 6  Changed: 6  Warnings: 0
```

`users` table state after updating all rows:

| id  | username      | about             |
| :-- | :------------ |  :---------------- |
| 2   | shinobi       | 404 bio not found |
| 3   | java team six | 404 bio not found |
| 4   | tony          |  404 bio not found |
| 5   | shinobi       | 404 bio not found |
| 6   | java team six | 404 bio not found |
| 7   |  tony          | 404 bio not found |

## Update Specific Row

To update only a specific row, use the `WHERE` clause. Update the `about` column for the user with `id` 2:

```sql
UPDATE users SET about ='Hello World :)' WHERE id=2;
```

This targets a single row:

```
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings:  0
```

`users` table state after updating a single row:

| id  | username      | about             |
| :-- | :------------ | :---------------- |
| 2   | shinobi       | Hello World  :)    |
| 3   | java team six | 404 bio not found |
| 4   | tony          | 404 bio not found |
| 5   | shinobi       |  404 bio not found |
| 6   | java team six | 404 bio not found |
| 7   | tony          | 404 bio not found |

## Updating Records Using Another Table

Modify records in one table based on data from another table. This is achieved by joining or listing the tables involved in the `UPDATE` statement and specifying the join condition in the `WHERE` clause.

Update the `about ` field in the `users` table using corresponding data from the `prospect_users` table where usernames match:

```sql
update users, prospect_users
set users.about = prospect_users.about
where prospect_users.username  = users.username;
```