sql server create primary key on existing table code example

Example 1: add primary key to existing table sql

alter table Persion add primary key (persionId,Pname,PMID)

Example 2: sql primary key

A primary key allows each record in a table to be uniquely identified. There can only be one
primary key per table, and you can assign this constraint to any single or combination of columns.
However, this means each value within this column(s) must be unique.
Typically in a table, the primary key is an ID column, and is usually paired with the AUTO_
INCREMENT keyword. This means the value increases automatically as new records are created.
CREATE TABLE users (
id int NOT NULL AUTO_INCREMENT,
first_name varchar(255),
last_name varchar(255) NOT NULL,
address varchar(255),
email varchar(255),
PRIMARY KEY (id)
);

Example 3: sql primary key

-- NOTE: this is for SQL-Oracle specifically

-- example:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = 'CUSTOMERS' 
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner;

-- syntax:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = '<table-name>' -- Replace <table-name> with your table-name
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner;

Example 4: sql server add primary key to existing table with data

ALTER TABLE Production.TransactionHistoryArchive
   ADD CONSTRAINT PK_TransactionHistoryArchive_TransactionID PRIMARY KEY CLUSTERED (TransactionID);