Changing data using UPDATE

You can use the UPDATE statement, followed by the name of the table or view, to change single rows, groups of rows, or all rows in a table. As in all data modification statements, you can change the data in only one table or view at a time.

The UPDATE statement specifies the row or rows you want changed and the new data. The new data can be a constant or an expression that you specify or data pulled from other tables.

If an UPDATE statement violates an integrity constraint, the update does not take place and an error message appears. For example, if one of the values being added is the wrong data type, or if it violates a constraint defined for one of the columns or data types involved, the update does not take place. See Table 7-4 in the section “Data conversions in IQ” for details on data type conversions for the UPDATE statement.

UPDATE syntax

For complete syntax, see UPDATE statement in Reference: Statements and Options. A simplified version of the syntax is:

UPDATE table-name

SET column_name = expression

WHERE search-condition

If the company Newton Ent. (in the Customers table of the sample database) is taken over by Einstein, Inc., you can update the name of the company using a statement such as the following:

UPDATE Customers
SET company_name = 'Einstein, Inc.'
WHERE company_name = 'Newton Ent.'

You can use any condition in the WHERE clause. If you are not sure how the company name was entered, you could try updating any company called Newton, with a statement such as the following:

UPDATE Customers
SET company_name = 'Einstein, Inc.'
WHERE company_name LIKE 'Newton%'

The search condition need not refer to the column being updated. The company ID for Newton Entertainments is 109. As the ID value is the primary key for the table, you could be sure of updating the correct row using the following statement:

UPDATE Customers
SET company_name = 'Einstein, Inc.'
WHERE id = 109

The SET clause

The SET clause specifies the columns to be updated, and their new values. The WHERE clause determines the row or rows to be updated. If you do not have a WHERE clause, the specified columns of all rows are updated with the values given in the SET clause.

You can provide any expression of the correct data type in the SET clause.

The WHERE clause

The WHERE clause specifies the rows to be updated. For example, the following statement replaces the One Size Fits All Tee Shirt with an Extra Large Tee Shirt

UPDATE Products
SET size  = 'Extra Large'
WHERE name = 'Tee Shirt' 
   AND size = 'One Size Fits All'

The FROM clause

You can use a FROM clause to pull data from one or more tables into the table you are updating. You can also employ a FROM clause to use selection criteria against another table to control which rows are updated.