SQL DELETE Statement

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The SQL DELETE statement is used to delete records from a database table. It allows you to remove one or more rows from a table that match a specified condition. Here’s the basic syntax for the DELETE statement:

DELETE FROM table_name
WHERE condition;

Let’s break down the syntax:

  • DELETE FROM: This is the clause that specifies the table from which you want to delete records.
  • table_name: This is the name of the table from which you want to delete records.
  • WHERE: This is an optional clause that allows you to specify a condition for deleting records. It determines which rows should be deleted based on the condition.
  • condition: This is the condition that must be met for a row to be deleted. It can include one or more conditions using comparison operators (e.g., =, <>, >, <, >=, <=) and logical operators (e.g., AND, OR, NOT).

Here’s an example that demonstrates the usage of the DELETE statement:

DELETE FROM employees
WHERE department = 'HR';

This example deletes all rows from the “employees” table where the department is ‘HR’. Be cautious when using the DELETE statement, as it permanently removes data from the table. It’s always recommended to take a backup or use transactions to ensure data integrity.

Deleting Single Record:

To delete a single record from a database table using the SQL DELETE statement, you need to specify a condition that uniquely identifies the record you want to delete. Here’s an example:

DELETE FROM table_name
WHERE column_name = value;

Let’s break down the example:

  • DELETE FROM: This is the clause that specifies the table from which you want to delete the record.
  • table_name: This is the name of the table from which you want to delete the record.
  • WHERE: This is the clause that allows you to specify a condition for deleting the record.
  • column_name: This is the name of the column that you want to use for identifying the record.
  • value: This is the specific value in the column that uniquely identifies the record you want to delete.

Here’s a more concrete example:

Suppose we have a table called “employees” with columns “employee_id” and “employee_name,” and we want to delete the record for an employee with the ID of 123:

DELETE FROM employees
WHERE employee_id = 123;

This statement will delete the row from the “employees” table where the “employee_id” is 123. Only the record that meets the condition will be deleted.

Deleting Multiple Record:

To delete multiple records from a database table using the SQL DELETE statement, you can use various conditions to identify the records you want to delete. Here’s an example:

DELETE FROM table_name
WHERE condition;

Let’s break down the example:

  • DELETE FROM: This is the clause that specifies the table from which you want to delete records.
  • table_name: This is the name of the table from which you want to delete records.
  • WHERE: This is the clause that allows you to specify conditions for deleting records.
  • condition: This is the condition or set of conditions that determine which rows should be deleted.

Here’s a more concrete example:

Suppose we have a table called “employees” with columns “employee_id,” “employee_name,” and “department,” and we want to delete all employees who are in the “HR” department:

DELETE FROM employees
WHERE department = 'HR';

This statement will delete all rows from the “employees” table where the “department” column is ‘HR’. All records that meet the specified condition will be deleted.

You can combine multiple conditions using logical operators such as “AND” or “OR” to delete records that meet more complex criteria. For example, to delete all employees in the “HR” department who have been inactive for more than one year:

DELETE FROM employees
WHERE department = 'HR' AND last_activity_date < DATE_SUB(NOW(), INTERVAL 1 YEAR);

Remember to exercise caution when deleting multiple records, as the operation cannot be undone, and data will be permanently removed from the table. Always backup data and double-check the conditions before executing the delete operation.

Delete all of the records:

To delete all records from a database table using the SQL DELETE statement, you don’t need to specify a condition. Instead, you can simply use the following syntax:

DELETE FROM table_name;

Let’s break down the example:

  • DELETE FROM: This is the clause that specifies the table from which you want to delete records.
  • table_name: This is the name of the table from which you want to delete all records.

Here’s an example:

Suppose we have a table called “employees” with columns “employee_id,” “employee_name,” and “department,” and we want to delete all records from this table:

DELETE FROM employees;

This statement will delete all records from the “employees” table. It removes all rows, effectively emptying the table.

Please exercise extreme caution when performing this operation, as deleting all records is irreversible and permanently removes data from the table. Always make sure you have a backup of the data or have taken the necessary precautions before executing this statement.