Type
|
Action
|
---|---|
CHECK
|
ensures that a specific
set or range of values are the only values in a column. It can also
check the validity of a value in one column based on a value in another
column within the same row.
|
NOT NULL
|
guarantees that a column
has nonmissing values in each row.
|
UNIQUE
|
enforces uniqueness
for the values of a column.
|
PRIMARY KEY
|
uniquely defines a row
within a table, which can be a single column or a set of columns.
A table can have only one primary key. The PRIMARY KEY constraint
includes the attributes of the NOT NULL and UNIQUE constraints.
|
FOREIGN KEY
|
specifies variables
whose values are linked to the values of the primary key variables
in another data set. This parent/child relationship limits modifications
that are made to both tables.
|