ORDER BY and LIMIT are two clauses that we have discussed above. MySQL DELETE Using ORDER BY And LIMIT Clause The Output of the query below shows that 0 row(s) have been returned, implying that the record has been deleted by the execution of the DELETE statement above. The output results show NULL value for all the columns, implying that no record exists for such an empNum. In order to verify the output of this DELETE statement, let’s execute the SELECT statement on this table with the empNum as 1013. In order to avoid such situations, in production, there is a practice of periodic data backups or unloads. If the WHERE clause is incorrect or if you miss out on having a WHERE clause then it may result in data loss. Please be very sure, about the WHERE clause here. The output statement below shows the time at which the statement was executed, the MySQL statement that was executed and the number of rows that were affected. Here we will try and remove an employee named ‘Chris Nolan’ with the employee number as 1013.Īs depicted in the picture above, the DELETE statement has been executed successfully and deleted one row from the employee’s table. Let’s go through the delete statement and its execution in detail. This could be further used to delete a set of similar kinds of rows from the table. The first and easier way of deleting records from the table in deleting the records one-by-one, using a very strong WHERE clause that ensures only one suitable record is deleted. Start_date: Holds date values for the joining date of the employee.ĭeptNum: Holds varchar for the department ID within an organization.Ĭity: Holds the name of the city in which the departments work from.Ĭountry: Holds the name of the country corresponding to the city.īonus: Holds the percentage value of the bonus. Start_date: Holds the date values for the joining date of the employee.ĮmpNum: Holds the integer values for employee number. Salary: Holds decimal values of the salary of each employee. LastName: Holds varchar values for the last name of the employee.įirstName: Holds varchar values for the first name of the employee.Įmail: Holds varchar values for the email ID of the employee.ĭeptNum: Holds varchar for the department ID that an employee belongs to. Given below is a sample table created in MYSQL.ĮmpNum: Holds integer values for the employee number. In such examples, it’s not advisable to use QUICK. When a new employee joins, he/she will get a new employee number and not the same number of the person who left. If we use the QUICK clause then the corresponding index space will remain unutilized. Whenever an employee leaves an organization, we need to delete the corresponding record. If we use the QUICK keyword, then the corresponding index space remains unutilized and can be utilized when new records that suit the index range that was deleted earlier are inserted.įor Example, consider an employee table where the employee ID is the index. Reclaiming the space at the time of execution of the DELETE statement consumes the processor time. Whenever we delete a row, the corresponding index also gets deleted. This also helps in avoiding table locking issues. This helps in achieving consistency across all the other operations that will be performed on that table. This modifier informs the MySQL Engine to delay the execution of the DELETE statement until such a time when there are no connections reading from the table that we are attempting to DELETE from.

It puts a limit on the number of rows that the DELETE statement can remove from the table. LIMIT clause follows the ORDER BY clause.Followed by the WHERE clause is the ORDER BY clause, which enforces the rows to be deleted in a particular order, either ascending or descending, on a column(s).

Next, we can mention any condition that controls the eligibility of the rows to be deleted.

We can mention one or more than one table names here. This is also mandatory and cannot be omitted.

Next comes the name of the table in which the DELETE operation has to be performed.

This is a mandatory keyword and cannot be omitted.

The syntax starts with the keyword “DELETE FROM”, thereby informing the MySQL Server about the type of activity to be performed.

We can later use this backup to restore the table in case of any mistakes. Thus, in order to avoid scenarios where a row is deleted by mistake, it’s advisable to take a backup of the table before executing the DELETE statement. Any row or multiple rows that we delete using the DELETE command can never be retrieved. There is an important factor to keep in mind before we proceed ahead.

Referential Integrity And Its Impact On DELETE.

Difference Between TRUNCATE And DELETE Statements.

MySQL DELETE Using ORDER BY And LIMIT Clause.

Mysql delete column