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Using the Update statement in SQL - Server

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

This part of the UPDATE statement specifies the table that will be updated

The SET clause specifies the column names and new data values to store in the column

Change the values in the specified columns in all the rows in the table.

When a customer purchases a book from the VirtualBookShelf.com website, the application should decrease the Qty column by the number purchased.

The SET clause specifies the column name and new value. In this example, 1 is subtracted from the current value of Qty and the result is stored in the Qty column.

Where clause specifies the row. This statement reduces the Qty column by one in each row where the book title is.

This example assumes only one book of the specified title was purchased, so setting the new value with the expression Qty = Qty -1 is appropriate.

Portion of the BookTable before the UPDATE statement is executed.

Here is the BookTable after the UPDATE statement has executed.