Which property or function allows SQL to insert a field value?

The correct choice, which is auto-increment, is significant because it specifically pertains to the way a database can automatically generate a sequential value for a field, typically a primary key. This function is used when defining a column within a table, allowing for automatic assignment of unique values to new records.

When a new row is added to a table, instead of requiring the user to manually provide a value for the auto-increment field, the database management system generates the next sequential number automatically. This is particularly useful for maintaining the uniqueness of primary key fields without user intervention, improving data integrity and simplifying data entry processes.

Other options do not directly relate to the function of inserting values in the context of generating unique identifiers. Composite refers to a primary key that consists of two or more columns, simple refers generally to a data type that is atomic and not composite, while numeric relates to a category of data types rather than a specific field insertion function.