LEGGERE PRIMARY KEY TRAMITE QUERY SELLE INFORMAZIONI DELLA TABELLA

USE tempdb;

CREATE TABLE dbo.Students(
FirstName varchar(10) NOT NULL,
LastName varchar(10) NOT NULL,
BirthDate datetime NOT NULL,
CONSTRAINT PK_Students PRIMARY KEY(FirstName, LastName)
);

SELECT
      COLUMN_NAME
  , DATA_TYPE
  , CHARACTER_MAXIMUM_LENGTH
  , NUMERIC_PRECISION
  , NUMERIC_SCALE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Students';

/* Output:

COLUMN_NAME  DATA_TYPE  CHARACTER_MAXIMUM_LENGTH NUMERIC_PRECISION NUMERIC_SCALE
------------ ---------- ------------------------ ----------------- -------------
FirstName    varchar    10                       NULL              NULL
LastName     varchar    10                       NULL              NULL
BirthDate    datetime   NULL                     NULL              NULL

(3 row(s) affected)

*/

SELECT CCU.COLUMN_NAME 
FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS CCU 
JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS TC 
ON CCU.CONSTRAINT_NAME = TC.CONSTRAINT_NAME 
WHERE CCU.TABLE_NAME = 'Students' AND 
CCU.TABLE_SCHEMA = 'dbo' AND 
TC.CONSTRAINT_TYPE = 'PRIMARY KEY';

/* Output:

COLUMN_NAME
------------
FirstName
LastName

(2 row(s) affected)

*/

DROP TABLE dbo.Students;