Oracle Add, modify non-null constraints

A NOT NULL constraint is a non-null constraint that often adds a non-null constraint when creating a table to guarantee that the field must enter a value

(1) Add NOT NULL constraint when creating table

Grammar:

CREATE Table table name (field type not NULL ...);

Instance:

CREATE TABLE Managerinfo (ManagerID VARCHAR2 (Ten), LOGINNAME VARCHAR2 (Ten) not Null,password VARCHAR2 (Ten) not null,name VARCHAR2 (+), TEL VARCHAR2 (11));

(2) Adding a non-empty constraint using alter

Grammar:

ALTER table name modify column not NULL;

Instance:

--use ALTER to add a non-empty constraint to the Name column

ALTER TABLE managerinfo MODIFY NAME not NULL;

(3) non-null constraint deletion

Simply change the column to null using the non-empty modify

Grammar:

ALTER Table name Modify column NULL;

Instance:

--use ALTER to change the name to a null value

ALTER TABLE managerinfo MODIFY NAME NULL;

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Oracle Add, modify non-null constraints