In this blog post, we'll focus on the DELETE command, which allows us to remove rows from a table based on specified conditions.
Understanding the DELETE Command Syntax
The DELETE command in PostgreSQL has a straightforward syntax:
DELETE FROM table_name
WHERE condition;
DELETE FROMindicates that we want to delete data from a table.table_nameis the name of the table from which we want to delete the data.WHEREis an optional clause that specifies the condition for deleting rows. If omitted, all rows in the table will be deleted.
Examples of Using DELETE in PostgreSQL
Example 1: Deleting All Rows
Let's start by deleting all rows from a table named "employees," which contains information about employees in a company. To delete all rows, we can use the following SQL command:
DELETE FROM employees;
Note: Be cautious when using this command, as it will delete all records from the "employees" table without any conditions.
Example 2: Deleting Rows Based on a Condition
Suppose we want to delete employees who no longer work for the company and have a "resigned" status in the "employment_status" column. The following SQL command achieves this:
DELETE FROM employees
WHERE employment_status = 'resigned';
This command will remove all rows from the "employees" table where the value of the "employment_status" column is 'resigned.'
Example 3: Deleting Rows Using Multiple Conditions
We can also delete rows based on multiple conditions. Let's say we want to delete employees who are both marked as "resigned" and have not logged in for more than a year. We can use the following SQL command:
DELETE FROM employees
WHERE employment_status = 'resigned' AND last_login_date < NOW() - INTERVAL '1 year';
This command deletes rows from the "employees" table that meet both conditions: "employment_status" is 'resigned,' and "last_login_date" is more than a year ago.