The purpose of the DELETE FROM statement is to delete one or more rows from a table.
Example: you want to delete rows in the table revenues
corresponding to the year 2010. The syntax is the following:
In this query:
- revenues is the table in which we delete the rows.
- where year=2014: we delete only rows for which year = 2014.
What happens if you do not put any where statement?”>
If you do not put any where statement, you will delete all rows in the table.
Will the rows be deleted permanently?
Yes, this command deletes the rows permanently. In a professional environment, information is not permanently deleted. Instead we use one of the following strategies:
- each customer data has a status. We change this status from “active” to “inactive” instead of deleting the data.
- if we ever delete a row, we make a copy of it in another database before deleting it.
Why deleting data to put it in another database?
Let us take the example of a website accessing data from a database. The more the rows in this database, the more time it takes for the website to retrieve data from it.
To improve the performance:
- we copy the data that is not useful to a database not accessed by the website (called an archive database).
- if the copy was successful, we delete this data from the database accessed by the website.
As a result:
- the data is not lost forever (it is present in the archive database).
- there are fewer rows in the database accessed by the website, which increases its performance.