I'm new to SQL and I'm trying to figure out what this NULL is doing. Here a simple example:
CREATE TABLE test (
bla VARCHAR NULL
);
So I tried to figure out wether this is set to be the default value, but it is null as default wether I put it there or not, right?
Also I wondered if it has to stay null (for whatever reason) but when I tried to insert a value it was possible anyway. So does it do anything?
From CREATE TABLE:
NULL
The column is allowed to contain null values. This is the default.
You could write:
INSERT INTO test(bla)
VALUES (NULL);
-- it holds NULL
INSERT INTO test(bla)
VALUES (default);
-- it holds NULL
INSERT INTO test(bla)
VALUES ('a');
-- it holds 'a'
You could also omit column:
CREATE TABLE test2(bla VARCHAR NULL, col2 INT NOT NULL);
INSERT INTO test2(col2) VALUES (1);
-- it contains NULL, 1
If you specify column as:
CREATE TABLE test(bla VARCHAR NOT NULL);
INSERT INTO test(bla) VALUES (NULL);
-- error
EDIT:
You don't have to specify NULL explicitly.
CREATE TABLE test(bla VARCHAR);
is the same as:
CREATE TABLE test (bla VARCHAR NULL);
You are parameterizing the column can be NULL
