SQL update statement

Last update on April 11 2024 10:01:32 (UTC/GMT +8 hours)

Update statement

Once there is some data in the table, it may be required to modify the data. To do so, the SQL UPDATE command can be used. It changes the records in tables.

The SQL UPDATE command changes the data which already exists in the table. Usually, it is needed to make a conditional UPDATE in order to specify which row(s) are going to be updated.

The WHERE clause is used to make the update restricted and the updating can happen only on the specified rows.

Without using any WHERE clause (or without making any restriction) the SQL UPDATE command can change all the records for the specific columns of a table.

Syntax:

UPDATE < table name > SET<column1>=<value1>,<column2>=<value2>,.....
WHERE <condition>;

Parameters:

Name	Description
table_name	Name of the table to be updated.
column1,column2	Name of the columns of the table.
value1,value2	New values.
condition	Condition(s) using various functions and operators.

Syntax diagram - UPDATE STATEMENT

Some important questions regarding the SQL UPDATE command

What is the SQL UPDATE command used for?

The SQL UPDATE command is used to modify existing records in a table in a database.

What does the WHERE clause do in an UPDATE statement?

The WHERE clause filters the rows in the table, specifying which records should be updated. If omitted, all rows in the table will be updated.

How can you update multiple columns using the UPDATE command?

You can update multiple columns by listing each column and its new value separated by commas in the SET clause.

What happens if you omit the WHERE clause in an UPDATE statement?

If the WHERE clause is omitted, all rows in the table will be updated, resulting in potential unintended consequences or data corruption.

How can you update data in one table based on values from another table?

You can use a JOIN operation in the UPDATE statement to update data in one table based on values from another table.

How can you verify that the update operation was successful?

After executing the UPDATE statement, you can check the number of rows affected to verify that the desired records were updated. Most database systems return the number of rows affected by the update operation.

SQL update for a specific column

Data for a specific column(s) can be changed with the SQL UPDATE statement.

Example:

Sample table: neworder

To change the value of 'ord_description' of 'neworder' table with 'ZOD', the following SQL statement can be used :

SQL Code:


-- This SQL code updates the 'ord_description' column in the 'neworder' table.
-- UPDATE statement begins
UPDATE neworder
-- Specifies the target table 'neworder' where the data will be updated
SET ord_description='ZOD';
-- Sets the value of the 'ord_description' column to 'ZOD' for all rows in the 'neworder' table

Explanation:

This SQL code uses the UPDATE statement to modify existing records in the 'neworder' table.

The UPDATE statement specifies the target table 'neworder' where the update operation will be performed.

The SET clause assigns the new value 'ZOD' to the 'ord_description' column for all rows in the 'neworder' table.

Since no WHERE clause is provided, the update operation will affect all rows in the table, setting the 'ord_description' column to 'ZOD' for each row.

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