SQL Delete Statement

Introduction

With the vast volumes of data to handle, data management can become difficult for any person or company. Anyone who handles data knows that occasionally, because of changes in real-world situations like any shift in the market, corporate affairs, personal data, etc., we must remove certain data from our database. For instance, a market research database deletes market analysis records frequently when any fluctuations or trends happen in a particular sector and new studies are carried out. To accomplish this, data management teams use the SQL delete command. A crucial component of this query language, SQL, is this command.

In this article, I will discuss the statement delete in SQL in detail, including its purpose and syntax.

What is SQL Delete Statement?

SQL delete statement is a tool that manages data in relational databases. SQL deletes multiple rows permanently from a table. Delete in SQL deletes rows from a table. The SQL delete command is a component of the Data Manipulation Language, a sub-language of SQL that permits database modifications.

The Importance of Delete Statements in SQL

Delete in SQL is essential for data accuracy, data cleaning, storage optimization, and regulatory compliance. So, let’s discuss everything in detail to learn more about it.

Data Accuracy

Data management is a task that requires accuracy because everything depends on the data that’s provided for work. If the data is inaccurate, it affects the whole work, and everyone's hard work will be wasted. This is where the importance of delete in SQL lies. It is used to maintain data accuracy. If something wrong gets fed into the database, we can easily remove it.

Data Cleaning

Data cleaning is so important in the process of managing data properly. Many times, a data set may contain duplicate data due to human error during data entry or the combining of different data sets. To avoid duplicate elements, we can use duplicate records in SQL.

Storage optimization

Sometimes our storage can become full, but if we delete something from this that is not so important, we can easily manage the storage space.

Syntax of SQL Delete Statement 

The basic syntax for the delete statement is as follows:

SQL

DELETE FROM table_name 

WHERE condition;

Let’s understand how to do it because it’s very important to do it rightly to get the proper result:

DELETE: This is the main keyword to operate the delete task in SQL; without it, it is not possible for SQL to delete table values.

FROM: This keyword provides the exact place or from which row the data should be deleted.

table_name: Replace it with the exact name of the table

WHERE (Optional): It is used to specify the condition that filters the rows to be deleted. If it is not applied, then all the rows will be deleted. So, if only specific rows need to be deleted, do not forget to apply it.

Condition: This is used just to check if the data is true or false, whatever the condition provides. The data will be deleted only if the condition is true. If the condition is false, then this data will remain the same.

To use the delete statement, we first need to connect to the database using a tool such as MySQL Workbench or SQL Server Management Studio. Then, we can select the desired database and table and click on the Execute button to run the statement.

 Using Logical Operators

Logical operators like AND, OR, and NOT can be used with the WHERE clause to further refine the delete statement. These operators help in creating complex conditions that can be used to delete specific rows.

For example, using the AND operator, we can delete records that match multiple conditions while using the OR operator, we can delete records that match at least one of the specified conditions.

Examples of SQL Delete Statement

Some examples of the SQL delete statement for different conditions are given below.

Example 1: Deleting All Rows

SQL

DELETE FROM buyers;

This statement will permanently remove all rows from the “buyers” table.

Example 2: Deleting Specific Rows

SQL 

DELETE FROM customers

WHERE customerID = 123

This deletes the row with the customerID of 123 from the “customers” table.

Example 3: Conditional Deletion

SQL

DELETE FROM Items

WHERE Price < 100 AND StockLevel = 0;

This deletes products whose price is less than 100 and stock is 0 from the “Items” table.

Truncate vs. Delete: Understanding the Differences

The truncate and delete statements perform the same work of removing data from a table, but there are some key differences to consider:

Delete: This statement offers some control on delete by specifying some conditions using WHERE, which can target specific rows for deletion.

Truncate: This statement has no control, which means that SQL deletes all records from the table quickly. It makes the table empty without going through individual row deletions.

When to Use Delete?

The delete statement checks every row individually, so if we want to delete any specific row, the delete statement can be used. If we use any other alternative, we might lose all the data in the table. So, when we only want to remove one row or any specific rows, we can use the delete statement.

When to Use Truncate?

The truncate statement does not work on individual rows, so we only use the statement when we want SQL to delete the rows entirely. One advantage of this is that it works fast, making it easy for us to work.

Drop vs. Delete: Understanding the Differences

Both Drop and Delete in SQL commands are used to remove data from a table. However, they have distinct differences in their functionality.

Drop

Drop is a DDL (Data Definition Language) command used to remove an entire table from the database. It permanently removes the table and all of its data.

The syntax for the drop command is:DROP TABLE table_name;

Some important points to note about the DROP command are:1. It cannot be undone, so be cautious when using this command.2. It requires the user to have drop privileges on the table.

 SQL Delete Table Command

SQL deletes a table from the database when we use the DROP TABLE statement. 

For example, if we have a table called 'products' and we want to delete it, we can use the following query:DROP TABLE products;This will delete the entire 'products' table from our database.

Delete

Delete is a DML (Data Manipulation Language) command used to remove one or more rows from a table. It only removes the specified rows and does not drop the entire table. The syntax for the DELETE command is:DELETE FROM table_name WHERE condition;

SQL Delete Row Query

To delete a specific row from a table in SQL, we can use the DELETE statement with a WHERE clause. For example, if we have a table called 'customers' and we want to delete the row with ID 5, we can use the following query:DELETE FROM customers WHERE id = 5;This will delete the row with ID 5 from the 'customers' table.

 Join Delete SQL:

To delete rows from a table based on a condition in another table, we can use the Delete Join statement. For example, if we have two tables 'employees' and 'salaries' and we want to delete all the employees with a salary greater than 100,000, we can use the following query:DELETE employees FROM employees INNER JOIN salaries ON employees.id = salaries.employee_id WHERE salaries.salary > 100000;This will delete all the employees from the 'employees' table whose salary is greater than 100,000, by joining the two tables on the employee_id column.

Column Delete in SQLTo delete a column in SQL, we can use the Alter Table statement. For example, if we have a table called 'employees' and we want to delete the 'salary' column, we can use the following query:ALTER TABLE employees DROP COLUMN salary;This will remove the 'salary' column from the 'employees' table.

Common Errors Using the Delete Statement and How to Avoid Them

Here are some errors that mostly happen at the time of using the delete statement:

Accidental Deletion of All Rows

It’s important to double-check the WHERE clause; otherwise, all the data will be deleted and all data will be lost. So, this is the thing we have to avoid before using a delete statement.

 Insufficient Permissions

Always ensure that we have permission to check or change a target table. Otherwise, after creating a table, we may have to face many problems.

How to Avoid the Common Errors?

Here are some tips to avoid the common errors with the use of the delete statement.

Test Queries in a Quiet Environment

Always work in a quiet place because if we have a silent atmosphere, it becomes easier for us to check properly.

Perform Backups Before Executing the Delete Statement

It’s become very important to perform backups before executing the delete statement. While doing this, we can restore anything easily and properly, and if there’s any error, anyone can restore it at any time.

There are specific scenarios where the delete statement is not used properly, for example, so many people forget to apply the WHERE clause sometimes, and then the whole table gets deleted, which is a waste of time and again needs to be made. 

Alternatives to the SQL Delete Statement

While the delete statement is the most effective statement to remove data, there are some other alternatives. We can use truncate rather than the delete statement, it is the most effective way to delete all data quickly. One more option we can use is dropping tables. This method may be faster, but it also has its limitations.

Conclusion

The SQL delete statement is a powerful tool in database management. It allows users to remove unwanted records and maintain data properly. By understanding its syntax, using the WHERE clause correctly, and following best practices, we can effectively use the SQL delete statement to manage our database.

FAQs

Q1. What is the delete command in SQL?

The delete command in SQL is used to remove one or more records from a table.

Q2. How do I delete a record in SQL?

To delete a record in SQL, we need to specify the table name and use a WHERE clause to specify the record we want to delete.

Q3. What is a DELETE table in SQL?

A DELETE table in SQL is a temporary table that stores the records that have been deleted from the original table.

Q4. How to delete from select SQL?

To delete from select SQL, we can use the DELETE command with a subquery in the WHERE clause to specify which records to delete.

Q5. Can we delete tables in SQL?

We can use the drop table command to delete tables in SQL.

Q6. How do I delete two rows in SQL?

To delete two rows in SQL, we can use the WHERE clause with the IN operator to specify the two rows that need to be deleted.

Q7. Is it ‘delete’ or ‘delete from’ SQL?

Both ‘delete’ and ‘delete from’ are valid syntax for deleting records in SQL. They can be used interchangeably.

Q8. Can we delete a row in SQL?

Yes, we can use the WHERE clause to specify a particular row that needs to be deleted in SQL.

Q9. How do I delete the last 10 rows in SQL?

To delete the last 10 rows in SQL, we can use the ORDER BY and LIMIT clauses to select the last 10 rows and then use the delete command to remove them.

Q10. Can we roll back delete in SQL?

Yes, we can use the rollback statement to undo or rollback the delete command and restore the deleted records. However, this will only work if the database is in a state where it can be rolled back.