A composite primary key is a primary key consisting of multiple columns. Microsoft usually refers to these as multicolumn primary keys in its documentation.
This article provides an example of creating a composite primary key using Transact-SQL in SQL Server.
A composite foreign key is a foreign key consisting of multiple columns.
This article provides an example of creating a composite foreign key using Transact-SQL in SQL Server.
In this article I demonstrate how to create a foreign key in SQL Server using Transact-SQL. I demonstrate how to create a foreign key at the time of creating the table (as opposed to updating an existing table).
A foreign key is a column that references another table’s primary key column. This creates a relationship between the tables.
This article presents eleven different approaches to retrieving foreign key information in SQL Server. Some of these will be more useful than others, depending on the situation.
Some of these methods can be modified to return further information. For example, you could perform joins on various system views to return more data.
There are often many ways to do the same (or similar) thing in SQL Server. Retrieving all primary keys from a database (or even just the primary key for a given table) is a case in point.
This article presents eleven different approaches to retrieving primary key information in SQL Server.
Some of these will be more useful than others, depending on your exact situation.
This article demonstrates how to create a primary key in SQL Server when creating a table using Transact-SQL.
A primary key is one or more columns that have been configured as the unique identifier for a given table. Primary keys can be used to enforce data integrity in the table.
A table can only have one primary key, and primary keys can only be added to columns that are defined as NOT NULL.
This article demonstrates how to create a primary key in a new table (i.e. when creating the table). If you need to create a primary key in an existing table, see How to Add a Primary Key to an Existing Table in SQL Server.
This article demonstrates how to add a primary key to an existing table in SQL Server using Transact-SQL.
A primary key is a column that has been configured as the unique identifier for a given table.
You would normally create a primary key constraint when you create the table, but you can also add a primary key to an existing table.
Note that a table can only have one primary key. So you can’t add a primary key if the table already has one.
Also primary keys can only be added to columns that are defined as NOT NULL.
In addition to the many data types available in SQL Server, you also have the option of creating your own data type. Some of these are referred to as “user-defined data types”, while others are referred to as “alias data types”.
A user-defined data type is implemented through a class of an assembly in the Microsoft.NET Framework common language runtime (CLR).
An alias data type is based on a SQL Server native system type. In other words, you use an existing data type for the basis of your alias data type.
Having said that, I’ve seen Microsoft use the term “user-defined data type alias” when referring to an alias data type. I’ve also seen it referred to as simply a “data type alias”.
Either way, this article demonstrates how to a create a user-defined data type alias using Transact-SQL.
This article highlights the main differences between the datetime and datetimeoffset data types in SQL Server.
Both data types are used for storing date and time values. But there are significant differences between the two.
Perhaps the most obvious difference is that the datetimeoffset stores the time zone offset, whereas datetime doesn’t.
Another important difference is that datetimeoffset allows you to specify the precision (up to 7 decimal places). This means that datetimeoffset values can vary in their storage size, depending on the precision being used.
The datetime type on the other hand, has a fixed storage size and precision.
This article looks at the main differences between the datetime2 and datetimeoffset data types in SQL Server.
Both data types are used for storing date and time values. Both are very similar, but with one key difference; the datetimeoffset stores the time zone offset.
This also results in datetimeoffset using more storage space than datetime2, so you would only use datetimeoffset if you need the time zone offset.