“not null”和“not null enable”有区别吗？

Question

When we define a table in Oracle we may define the columns as:

"NAME" VARCHAR2(80) NOT NULL ENABLE

My question is I could not understand the meaning of "ENABLE" in this statement. What would be the difference if we just define as "NAME" VARCHAR2(80) NOT NULL ?

Answer 1

ENABLE is the default state, so leaving it out has the same effect. The opposite would be to specify DISABLE , in which case the constraint would not be active.

See the constraint documentation for more information.

Answer 2

For example (1)

CREATE TABLE FOO (PRIORITY_LEVEL NUMBER DEFAULT 42 NOT NULL ENABLE);

is the same with

CREATE TABLE FOO (PRIORITY_LEVEL NUMBER DEFAULT 42 NOT NULL);

(2)

CREATE TABLE FOO (PRIORITY_LEVEL NUMBER DEFAULT 42 NOT NULL DISABLE);

in general, is the same with

CREATE TABLE FOO (PRIORITY_LEVEL NUMBER NULL);