Summary: in this tutorial, we will show you what the primary key is and how to manage PostgreSQL primary key constraints through SQL statements.
Aug 31, 2016 When creating a table in Microsoft Access it is important that the table is correctly setup with a primary key that auto-increments. Without this the table will be difficult to input and output data. Notes: Only one field in a table can be the primary key and/or auto-increment. MySQL query to create a table with auto-incremented column. CREATE TABLE Sales( ID INT PRIMARY KEY AUTOINCREMENT, ProductName VARCHAR (20) NOT NULL, CustomerName VARCHAR (20) NOT NULL, DispatchDate date, DeliveryTime timestamp, Price INT, Location varchar(20) ); Example. Summary: in this tutorial, we will show you what the primary key is and how to manage PostgreSQL primary key constraints through SQL statements. A primary key is a column or a group of columns used to identify a row uniquely in a table. You define primary keys through primary key constraints.
A primary key is a column or a group of columns used to identify a row uniquely in a table.
Office 2013 product key generator free download pdf. You define primary keys through primary key constraints. Technically, a primary key constraint is the combination of a not-null constraint and a UNIQUE constraint.
A table can have one and only one primary key. It is a good practice to add a primary key to every table. When you add a primary key to a table, PostgreSQL creates a unique B-tree index on the column or a group of columns used to define the primary key.
Define primary key when creating the table
Normally, we add the primary key to a table when we define the table’s structure using CREATE TABLE statement.
The following statement creates a purchase order (PO) header table with the name
po_headers .
The
po_no is the primary key of the po_headers table, which uniquely identifies purchase order in the po_headers table.
In case the primary key consists of two or more columns, you define the primary key constraint as follows:
For example, the following statement creates the purchase order line items table whose primary key is a combination of purchase order number (
po_no ) and line item number ( item_no ).
If you don’t specify explicitly the name for primary key constraint, PostgreSQL will assign a default name to the primary key constraint. By default, PostgreSQL uses
table-name_pkey as the default name for the primary key constraint. In this example, PostgreSQL creates the primary key constraint with the name po_items_pkey for the po_items table.
In case you want to specify the name of the primary key constraint, you use
CONSTRAINT clause as follows:
Define primary key when changing the existing table structure
It is rare to define a primary key for existing table. In case you have to do it, you can use the ALTER TABLE statement to add a primary key constraint.
The following statement creates a table named
products without defining any primary key.
Suppose you want to add a primary key constraint to the
products table, you can execute the following statement:
How to add an auto-incremented primary key to an existing table
Suppose, we have a
vendors table that does not have any primary key.
And we add few rows to the
vendors table using INSERT statement:
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To verify the insert operation, we query data from the
vendors table using the following SELECT statement:
Now, if we want to add a primary key named
id into the vendors table and the id field is auto-incremented by one, we use the following statement:
Let’s check the
vendors table again.
Remove primary key
To remove an existing primary key constraint, you also use the
ALTER TABLE statement with the following syntax:
For example, to remove the primary key constraint of the
products table, you use the following statement:
In this tutorial, you have learned how to add and remove primary key constraints using
CREATE TABLE and ALTER TABLE statements.
Re: How To Auto Increment Alphanumeric Primary Key In sql server 2008
Jul 12, 2013 12:52 AM|RagavanB|LINK
Hi Manish,
try like this sample,
Personal detail:
create table personaldetail(id bigint identity primary key,pid nvarchar(20) unique,name nvarchar(25),addres nvarchar(100))
Occupation:
create table occupation(id bigint identity primary key,pid nvarchar(20) references personaldetail(pid),occupation nvarchar(25),dept nvarchar(25))
then generate the pid at code behind like,
Auto Generate Primary Key Sql Server
public string generate_ID(){
int id=0;
string pid;
string pidquery = 'select top 1 SUBSTRING(pid,4,len(piid))as pid from personal detail order by pid desc';
// here 4 char denotes number after prefix string('HUA')
Sql Create Table Auto Increment
SqlCommand scmd = new SqlCommand(pidquery, con);
SqlDataAdapter adapter = new SqlDataAdapter(pidquery, con); DataTable restable = new DataTable(); adapter.Fill(restable); if (restable.Rows.Count > 0) { SqlDataReader reader = scmd.ExecuteReader(); reader.Read(); id= Convert.ToInt32(reader['pid']); id= id+ 1; pid = 'HUA' + Convert.ToString(id); } else // its for if no data in db { id= 1; pid = 'HUA' + Convert.ToString(jid); }
return pid;
Auto Generate Primary Key Sql Definition
}
after got id:
insert into both tables like:
Mysql Identity Column
1. insert into personaldetail('+pid+','+name+','+addr+')
2.insert into occupation('+pid+','+occupation+','+dept+')
please let me know the status.
Ms Sql Auto Increment
Thank you,
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