Category: DBMS

Database Management Systems

Create a Computed Column that Uses Data from Another Table in SQL Server

Posted on by Ian

A widely known limitation of computed columns in SQL Server is that they can’t access data from other tables. That is, your expression can use columns in the same table, but not from other tables.

But this is only half-true. While you can’t reference another table’s column directly within your expression, you can invoke a user-defined function. And therefore, you could create a user-defined function that performs the calculation you need, then simply call that function as your computed column’s expression.

Here’s an example to demonstrate.

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Change an Existing Column to a Computed Column in SQL Server (T-SQL Example)

Posted on by Ian

This article demonstrates how to use T-SQL to change an existing column to a computed column in SQL Server.

A computed column is a virtual column that uses an expression to calculate its value. The expression will typically use data from other columns. A computed column is not physically stored in the table unless it’s marked PERSISTED.

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Add a Computed Column to an Existing Table in SQL Server

Posted on by Ian

This article demonstrates how to use T-SQL to add a computed column to an existing table in SQL Server.

A computed column is a virtual column that uses an expression to calculate its value. The expression will typically use data from other columns. A computed column is not physically stored in the table unless it’s marked PERSISTED.

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How @@MAX_CONNECTIONS Works in SQL Server

Posted on by Ian

In SQL Server, the @@MAX_CONNECTIONS configuration function returns the maximum number of simultaneous user connections allowed on an instance of SQL Server. The number returned is not necessarily the number currently configured.

No argument is required. You can simply use it in a SELECT statement to return the maximum number of simultaneous user connections allowed on the current server.

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