SQL Update

In this tutorial you will learn how to update records in a database table using SQL.

## Updating Table Data
In the previous chapters we've learnt how to insert data as well as how to select data from a database table based on various conditions. In this tutorial we'll learn to perform one more important task which is updating the existing records in a database table.

## Syntax
The UPDATE statement is used to update existing data in a table.

```sql
UPDATE table_name
SET column1_name = value1, column2_name = value2,...
WHERE condition;
```
Here, column1_name, column2_name,... are the names of the columns or fields of a database table whose values you want to update. You can also combine multiple conditions using the AND or OR operators, that you've learned in the previous chapters.

<div class="callout callout-danger mb-3">Warning: The WHERE clause in the UPDATE statement specifies which record or records should be updated. If you omit the WHERE clause, all the records will be updated.</div>

Let's check out some examples that demonstrate how it actually works.

Suppose we've an employees table in our database that has following records:

```sql
+--------+--------------+------------+--------+---------+
| emp_id | emp_name     | hire_date  | salary | dept_id |
+--------+--------------+------------+--------+---------+
|      1 | Ethan Hunt   | 2001-05-01 |   5000 |       1 |
|      2 | Tony Montana | 2002-07-15 |   6500 |       5 |
|      3 | Sarah Connor | 2005-10-18 |   8000 |       3 |
|      4 | Rick Deckard | 2007-01-03 |   7200 |       4 |
|      5 | Martin Blank | 2008-06-24 |   5600 |    NULL |
+--------+--------------+------------+--------+---------+
```
## Updating a Single Column
The following SQL statement will update the emp_name field of the employees table and set a new value where the employee id i.e. emp_id is equal to 3.

```sql
UPDATE employees SET emp_name = 'Sarah Ann Connor'
WHERE emp_id = 3;
```
After execution, the resulting table will look something like this:

```sql
+--------+------------------+------------+--------+---------+
| emp_id | emp_name         | hire_date  | salary | dept_id |
+--------+------------------+------------+--------+---------+
|      1 | Ethan Hunt       | 2001-05-01 |   5000 |       1 |
|      2 | Tony Montana     | 2002-07-15 |   6500 |       5 |
|      3 | Sarah Ann Connor | 2005-10-18 |   8000 |       3 |
|      4 | Rick Deckard     | 2007-01-03 |   7200 |       4 |
|      5 | Martin Blank     | 2008-06-24 |   5600 |    NULL |
+--------+------------------+------------+--------+---------+
```
## Updating Multiple Columns
Similarly, you can update multiple columns using a list of comma-separated column name and value pair. The following example will update the salary and dept_id field of an existing employee in the employees table whose emp_id is 5.

```sql
UPDATE employees
SET salary = 6000, dept_id = 2
WHERE emp_id = 5;
```
After execution, the resulting table will look something like this: