Oracle Modify Constraints

Create a member Table

DROP TABLE member PURGE; CREATE TABLE member (    Mid         number,    name     VARCHAR2) ;

Modify Table Constraints

Syntax: ALTER table name ADD CONSTRAINT constraint name constraint type (field) [Other options]

To add a primary key constraint to a member table
ALTER TABLE member  ADD CONSTRAINT pk_mid PRIMARY KEY (mid);

Description: For the five constraints: the above syntax is used to check (check), unique (unique), primary key (PRIMARY key), foreign key (FOREIGN key) four class constraints.
If you want to add a non-null constraint to a table, there is only one way to do so, using the Modify table structure, such as
ALTER TABLE member  MODIFY (name VARCHAR2 () not NULL)

Delete Table constraint

Grammar ALTER TABLE DROP CONSTRAINT constraint name Delete member table PRIMARY KEY constraint ALTER TABLE DROP CONSTRAINT Pk_mid;

Oracle Modify Constraints