If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field. Note: It is very important to understand that a NULL value is different from a zero value or a field that contains spaces.
A field with a NULL value is one that has been left blank during record creation!
Here are the similarities and differences between Find and Replace and an update query: Like the Find and Replace dialog box, an update query lets you specify which value is being replaced, and what the new value is.
Unlike the Find and Replace dialog box, an update query lets you: As a best practice when creating an update query, first create a select query that identifies the records that you want to update, and then convert that query to an update query that you can run to update the records.
By selecting data first, you can verify that you’re updating the records you want before you actually change any data.
To add new records to a database you use an append query, and to delete whole records from a database you use a delete query.You use update queries in Access databases to add, change, or delete the information in an existing record.You can think of update queries as a powerful form of the Find and Replace dialog box.You cannot undo the results of an update query, and making a backup helps make sure that you can reverse your changes if you change your mind.When you need to update data from one table to another, consider the following rule: the data types for the source and destination fields must either match or be compatible.