UNIQUE INDEX
Most databases use a standardized format for building UNIQUE keys. The standard syntax does work on most databases. The following table displays how to create a UNIQUE key in the different database engines.
| SQL Syntax | Description | SQL Database |
| CREATE TABLE table_name (id INT NOT NULL,UNIQUE (id))
|
Creates a UNIQUE index when the table is created | MySQL, PostgreSQL |
| CREATE TABLE table_name (id INT NOT NULL,name VARCHAR(50) NOT NULL,UNIQUE (id, name)
)
|
Creates a UNIQUE index when the table is created | PostgreSQL |
| CREATE TABLE table_name (id INT NOT NULL UNIQUE) | Creates a UNIQUE index when the table is created | PostgreSQL, SQL Server, Oracle |
| CREATE TABLE table_name (id INT NOT NULL,CONSTRAINT unique_index_name UNIQUE(id))
|
Creates a UNIQUE index when the table is created | MySQL, SQL Server, Oracle |
| CREATE TABLE table_name (id INT NOT NULL CONSTRAINT unique_index_name UNIQUE) | Creates a UNIQUE index when the table is created | PostgreSQL |
