Omezení not-null a unique

Introduction to Relational Databases in SQL

Timo Grossenbacher

Data Journalist

Omezení not-null

CREATE TABLE students (
 ssn integer not null,
 lastname varchar(64) not null,
 home_phone integer,
 office_phone integer
);

NULL != NULL

Při vytváření tabulky...

CREATE TABLE students (
 ssn integer not null,
 lastname varchar(64) not null,
 home_phone integer,
 office_phone integer
);

Po vytvoření tabulky...

ALTER TABLE students 
ALTER COLUMN home_phone 
SET NOT NULL;

ALTER TABLE students 
ALTER COLUMN ssn 
DROP NOT NULL;

CREATE TABLE table_name (
 column_name UNIQUE
);

ALTER TABLE table_name
ADD CONSTRAINT some_name UNIQUE(column_name);

Introduction to Relational Databases in SQL