Effects of changing field types

Changing a field type changes the kind of data the field can contain. It also affects how you find and sort information that uses that field. For example, if you change a date field to a text field, you can type other information in the field besides a date, but you will no longer be able to sort chronologically.

When you change	This happens
A text field to a number, date, time, or timestamp field	The first 255 characters that can be converted are moved to the first line, deleting any remaining characters. Values that can't be used as dates or times are displayed and indexed as question mark (?). Date and time fields can't contain text.
A number, date, time, or timestamp field to a text field	Existing data isn't changed.
A container to another field type, or remove the option for global storage	Existing data in the field is deleted.
Any field to a container field or to a field with global storage	Existing data is deleted.
Any field type to a calculation or summary field	Existing data is replaced with the results of the formula or summary you specify.
A field used in a summary to a field type that can't be used in a summary	You see an alert. You must change the summary so it doesn't include the field or delete the summary field before changing the field type.
A field used in a relationship	You might not be able to change the field type if the field is used as a match field in a relationship and the new field type cannot be used as a match field in a relationship. Container fields cannot be used as match fields. Fields with global storage and summary fields cannot be used as key fields. Fields in which indexing is disabled cannot be used as key fields.