Adobe 38043740 Developing Applications - Page 414

DEVELOPING COLDFUSION 9 APPLICATIONS 409 Accessing and Using Data However, if the field does not support Nulls, specify a value for the field as part of the INSERT statement; otherwise, the database issues an error. The LastName and FirstName values in the query are contained within single-quotation marks. This is necessary because the table columns are defined to contain character strings. Numeric data does not require the quotation marks. Updating data in a database Use the UPDATE statement in SQL to update the values of a table row. Update lets you update the fields of a specific row or all rows in the table. The UPDATE statement has the following syntax: UPDATE table_name SET column_name1=value1, ... , column_nameN=valueN [ WHERE search_condition ] Note: There are additional options to UPDATE depending on your database. For a complete syntax description for UPDATE, see the product documentation. Do not attempt to update a record's primary key field. Your database typically enforces this restriction. The UPDATE statement uses the optional WHERE clause, much like the SELECT statement, to determine which table rows to modify. The following UPDATE statement updates the e-mail address of John Smith: UPDATE employees SET Email='[email protected]' WHERE EmpID = 51 Be careful using UPDATE. If you omit the WHERE clause to execute the following statement: UPDATE employees SET Email = '[email protected]' you update the Email field for all rows in the table. Deleting data from a database The DELETE statement removes rows from a table. The DELETE statement has the following syntax: DELETE FROM table_name [ WHERE search_condition ] Note: There are additional options to DELETE depending on your database. For a complete syntax description for DELETE, see the product documentation. You can remove all rows from a table using a statement in the form: DELETE FROM employees Typically, you specify a WHERE clause to the DELETE statement to delete specific rows of the table. For example, the following statement deletes John Smith from the table: DELETE FROM employees WHERE EmpID=51 Updating multiple tables The preceding examples describe how to modify a single database table. However, you might have a database that uses multiple tables to represent information. One way to update multiple tables is to use one INSERT statement per table and to wrap all INSERT statements within a database transaction. A transaction contains one or more SQL statements that can be rolled back or committed as a unit. If any single statement in the transaction fails, you can roll back the entire transaction, canceling any previous writes that occurred within the transaction. You can use the same technique for selects, updates, and deletes. The following example uses the cftransaction tag to wrap multiple SQL statements: Last updated 1/20/2012