I need to understand how to add a constraint statement to
create a check constraint for a table. How do you alter a
table to add a check constraint?
Check Constraints to validate values
Check constraints validate that values in a given column
meet a specific criteria. For example, you could create a check constraint on a
varchar2 column so it only can contain the values T or F as in this example:
( status_id NUMBER PRIMARY KEY,
person_id NUMBER NOT NULL,
active_record VARCHAR2(1) NOT NULL
person_ssn VARCHAR2(20) CONSTRAINT un_person_ssn
In this example we created a table called MY_STATUS
using the create table command. Notice the constraint keyword, this indicates
that we are getting ready to define a constraint. Recall that earlier in this
chapter we discussed in-line and out of line constraints. This particular
example is known as an in-line constraint because the constraint is being
defined in the same line as the column being defined.
If you need to add a check constraint to a table after
the fact, simply use the alter table command. Here is an example:
ALTER TABLE my_status ADD (CONSTRAINT ck_stats_01
CHECK (UPPER(active_record)='t? or
Expressions can be used with check constraints.
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