SQL DROP Columns & Rows: Tutorial

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  • 0:04 Drop Columns & Rows
  • 0:53 Remove a Column
  • 1:14 Some Examples
  • 1:48 Delete a Row of Data
  • 3:08 Lesson Summary
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Lesson Transcript
Instructor: Martin Gibbs

Martin has 16 years experience in Human Resources Information Systems and has a PhD in Information Technology Management. He is an adjunct professor of computer science and computer programming.

This lesson reviews the syntax for dropping columns and rows from a database using SQL. Deleting a column removes a data field; removing a row deletes a record of data.

DROP Columns & Rows

Drop it!

Perhaps one of the most visual of the SQL commands, DROP, does exactly what you think it would. It drops a table, a view, a column, or row. But not only does the command drop the object, any data associated with it's gone, as if you'd dropped it off a bridge into a river.

Before we dig into the syntax of the commands for dropping columns and/or rows, let's quickly review the database table structure:

In a database, the column refers to the data field, while the row is a record of data. In a database table, the columns spread across the screen, while the rows go down (think 'row-row-row your data gently down the table').

Sometimes there's a need in SQL to remove a column or a row from a table: Removing a column requires the ALTER TABLE command; deleting a row makes use of DELETE.

Remove a Column

In SQL Server and Oracle databases, the syntax is:

ALTER TABLE table_name DROP COLUMN column_name;

In MySQL, the syntax is:

ALTER TABLE table_name DROP column_name;

Note that all commands end with a semicolon ( ; ). This terminates the line, telling the computer that it should complete the command. If the semicolon is misplaced or omitted, the code will not function properly.

Some Examples

To apply to a real-world example, consider the figure Customer Table. The goal is to drop the SSN column because of a request from information security.

columns example

In SQL Server and Oracle databases, the syntax is:


In MySQL, the syntax is:

ALTER TABLE customer_data DROP SSN;

It's important to consider some things here, too. When you drop the column from the table, all of the data is deleted also! This can't be undone!

If the column is a primary key or a foreign key to another table, it cannot be deleted. You'll first have to remove these dependencies before deleting.

Delete a Row of Data

When dropping a row of data, you're in effect deleting that data record from the table and the database.

The syntax is as follows:

DELETE FROM table_name WHERE condition;

Note that the command uses the WHERE condition: This is required to specify which records are to be deleted.

In the table Customer Table 2, we'll remove the records for John Doe.

customer table 2

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