Union Auto Generate Primary Key View Sql Server

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Similar to MySQL, PostgreSQL, Oracle, and many other relational databases, SQL Server is best utilized when assigning unique primary keys to most database tables.

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The advantages to using numeric, auto incremented primary keys are numerous, but the most impactful benefits are faster speed when performing queries and data-independence when searching through thousands of records which might contain frequently altered data elsewhere in the table. With a consistent and unique numeric identifier, applications can take advantage of these faster and more reliable queries.

Basic Table Creation

Once connected to your SQL Server, you’d normally start by CREATING a new table that contains the the field you wish to use as your incremented primary key. For our example, we’ll stick with the tried and true id field:

This article answers questions about Auto-incremented ID with the VARCHAR / NVARCAHAR data type in SQL Server. Suppose I have an EmployeeMaster table and it has an EmployeeNo column with VARCHAR data type and I want to auto-generate EmployeeNo with some prefix like SEZ0000001, SEZ0000002, SEZ0000003 and so on. PRIMARY KEY (ID ASC. Auto increment Primary Key is used in SQL Server - to allow a unique and not null no to be generated when a new record is inserted in table for a particular tuple. There's no such thing as AUTONUMBER in SQL Server, What there is, is the IDENTITY property, which allows for the automatic creation of new records, such as for PKs, and IDENTITY is.

The problem here is, we have no way of controlling our id field. When a new record is inserted, we not only must manually enter a value for id, but we have to perform a query ahead of time to attempt to verify that id value doesn’t already exist (a near-impossibility when dealing with many simultaneous connections).

Using Identity and Primary Key Constraints

The solution turns out to be using two constraint options provided by SQL Server.

The first is PRIMARY KEY, which as the name suggests, forces the specified column to behave as a completely unique index for the table, allowing for rapid searching and queries.

While SQL Server only allows one PRIMARY KEY constraint assigned to a single table, that PRIMARY KEY can be defined for more than one column. In a multi-column scenario, individual columns can contain duplicate, non-unique values, but the PRIMARY KEY constraint ensures that every combination of constrained values will in fact be unique relative to every other combination.

The second piece of the puzzle is the IDENTITY constraint, which informs SQL Server to auto increment the numeric value within the specified column anytime a new record is INSERTED. While IDENTITYcan accept two arguments of the numeric seed where the values will begin from as well as the increment, these values are typically not specified with the IDENTITY constraint and instead are left as defaults (both default to 1).

With this new knowledge at our fingertips, we can rewrite our previous CREATE TABLE statement by adding our two new constraints.

That’s all there is to it. Now the id column of our books table will be automatically incremented upon every INSERT and the id field is guaranteed to be a unique value as well.

Summary: in this tutorial, you will learn how to use MySQL primary key constraint to create the primary key for a table.

Introduction to MySQL primary key

A primary key is a column or a set of columns that uniquely identifies each row in the table. The primary key follows these rules:

A primary key must contain unique values. If the primary key consists of multiple columns, the combination of values in these columns must be unique.
A primary key column cannot have NULL values. Any attempt to insert or updateNULL to primary key columns will result in an error. Note that MySQL implicitly adds a NOT NULL constraint to primary key columns.
A table can have one an only one primary key.

Because MySQL works faster with integers, the data type of the primary key column should be the integer e.g., INT, BIGINT. And you should ensure sure that value ranges of the integer type for the primary key are sufficient for storing all possible rows that the table may have.

A primary key column often has the AUTO_INCREMENT attribute that automatically generates a sequential integer whenever you insert a new row into the table.

Composite Primary Key Sql Server

When you define a primary key for a table, MySQL automatically creates an index called PRIMARY.

MySQL `PRIMARY KEY` examples

The PRIMARY KEY constraint allows you to define a primary key of a table when you create or alter table.

1) Define a `PRIMARY KEY` constraint in `CREATE TABLE`

Typically, you define the primary key for a table in the CREATE TABLE statement.

If the primary key has one column, you can use the PRIMARY KEY constraint as a column constraint:

Sql Add Primary Key

When the primary key has more than one column, you must use the PRIMARY KEY constraint as a table constraint.

In this syntax, you separate columns in the column_list by commas (,).

The PRIMARY KEY table constraint can be used when the primary key has one column:

The following example creates a table named users whose primary key is the user_id column:

This statement creates the roles table that has the PRIMARY KEY constraint as the table constraint:

In case the primary key consists of multiple columns, you must specify them at the end of the CREATE TABLE statement. You put a comma-separated list of primary key columns inside parentheses followed the PRIMARY KEY keywords.

The following example creates the user_roles table whose primary key consists of two columns: user_id and role_id. It defines the PRIMARY KEY constraint as the table constraint:

Note that the statement also created two foreign key constraints.

2) Define `PRIMARY KEY` constraints using `ALTER TABLE`

If a table, for some reasons, does not have a primary key, you can use the ALTER TABLEstatement to add a primary key to the table as follows:

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Pengertian Primary Key

The following example adds the id column to the primary key.

First, create the pkdemos table without a primary key.

Second, add a primary key to the pkdemos table using the ALTER TABLE statement:

If you add a primary key to a table that already has data. The data in the column(s), which will be included in the primary key, must be unique and not NULL.

`PRIMARY KEY` vs. `UNIQUE KEY` vs. `KEY`

KEY is the synonym for INDEX. You use the KEY when you want to create an index for a column or a set of columns that is not the part of a primary key or unique key.

Unique Key

A UNIQUE index ensures that values in a column must be unique. Unlike the PRIMARY index, MySQL allows NULL values in the UNIQUE index. In addition, a table can have multiple UNIQUE indexes.

Suppose that email and username of users in the users table must be unique. To enforce thes rules, you can define UNIQUE indexes for the email and username columns as the following statement:

Add a UNIQUE index for the username column: