Constraints provide a means to enforce data integrity. In addition to
NOT NULL, discussed earlier in this chapter, SQL Server provides five constraint types:
DEFAULT. These constraints help further define the type of data you can store in tables.
Constraints are covered in detail in Chapter 22, “Implementing Data Integrity.” This chapter introduces the basic means for adding constraints to a table. You can add constraints at the time of table creation, or you can add them after a table has been created by using the
ALTER TABLE statement.
Listing 20.11 shows a
CREATE TABLE statement that has an example of each one of the five constraint types listed. The
PRIMARY KEY ...