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Updating and Deleting Tables

SQL, or Structured Query Language, is a standard programming language designed for managing data in relational database management systems (RDBMS). In this tutorial, we will focus on how to update and delete tables in SQL.

Updating Tables in SQL​

The SQL UPDATE statement is used to modify the existing records in a table. It allows you to change the values of specified columns in all rows that satisfy the condition.

The basic syntax for UPDATE is as follows:

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Let's consider an example where we have a Customers table, and we want to update the customer's city to 'San Francisco' where the customer's ID is equal to 1.

UPDATE Customers
SET City = 'San Francisco'
WHERE CustomerID = 1;

In the above SQL statement:

  • UPDATE Customers is the command that tells SQL to update the Customers table.
  • SET City = 'San Francisco' is the command that tells SQL to update the City column with the value 'San Francisco'.
  • WHERE CustomerID = 1 is the condition that the specific record must meet for the update to apply.

Deleting Tables in SQL​

The SQL DELETE statement is used to delete existing records in a table. This command removes one or more records from a table.

The basic syntax for DELETE is as follows:

DELETE FROM table_name
WHERE condition;

For example, let's consider that we want to delete a record from the Customers table where the CustomerID is 1.

DELETE FROM Customers
WHERE CustomerID = 1;

In the above SQL statement:

  • DELETE FROM Customers is the command that tells SQL to delete from the Customers table.
  • WHERE CustomerID = 1 is the condition that the specific record must meet for it to be deleted.

Please be careful while using the DELETE statement without WHERE condition as it will delete all the records from the table.

Conclusion​

In this tutorial, you learned how to update and delete records from a table in SQL using the UPDATE and DELETE statements. Practice with your own examples to get a better understanding of how these commands work. Remember, always make sure you have a backup of your database before running UPDATE and DELETE commands, as they modify the data in your tables.