Data Updation

The UPDATE statement is the tool for modifying existing data in a table. You use it when a value in one or more columns of a record needs to be changed — for example, correcting a spelling, updating an address, or filling in a missing value.

The basic syntax is:

UPDATE table_name
SET attribute1 = value1, attribute2 = value2, ...
WHERE condition;

The WHERE clause is critical: it identifies exactly which row(s) should be updated. Without it, the change applies to every row in the table.

Example 1: Updating a single column for one row

In the STUDENT table, the student with roll number 3 has a NULL value in the GUID column. Because students with roll numbers 3 and 5 are siblings, we need to set the GUID for roll number 3 to 101010101010.

mysql> UPDATE STUDENT
    -> SET GUID = 101010101010
    -> WHERE RollNumber = 3;
Query OK, 1 row affected (0.06 sec)
Rows matched: 1  Changed: 1  Warnings: 0

The message Rows matched: 1 confirms that one row satisfied the WHERE condition. Changed: 1 means the value was actually modified. You can verify the result with SELECT * FROM STUDENT.

Example 2: Updating multiple columns for one row

Suppose the guardian with GUID 466444444666 has requested two changes: the address to 'WZ - 68, Azad Avenue, Bijnour, MP' and the phone number to '9010810547'. You can update both columns in a single UPDATE statement by separating the assignments with commas.

mysql> UPDATE GUARDIAN
    -> SET GAddress = 'WZ - 68, Azad Avenue,
    -> Bijnour, MP', GPhone = 9010810547
    -> WHERE GUID = 466444444666;
Query OK, 1 row affected (0.06 sec)
Rows matched: 1  Changed: 1  Warnings: 0

After the update, the GUARDIAN table looks like this: