In database terms, a CHECK constraint is a type of constraint that checks data before it enters the database.
CHECK constraints help maintain data integrity, because they prevent invalid data entering the database.
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How AUTOINCREMENT Works in SQLite
In SQLite, an AUTOINCREMENT column is one that uses an automatically incremented value for each row that’s inserted into the table.
There are a couple of ways you can create an AUTOINCREMENT column:
- You can create it implicitly when you define the column as
INTEGER PRIMARY KEY. - You can create it explicitly with the
AUTOINCREMENTkeyword. One downside of this method is that it uses extra CPU, memory, disk space, and disk I/O overhead.
Both methods cause the column to use an incrementing value each time a new row is inserted with NULL in that column.
However, there are some subtle differences between how each method works.
Introduction to Temporary Tables in SQL Server
In SQL Server, a temporary table is a certain kind of table that exists until goes out of scope (unless it’s explicitly dropped).
This is different to a regular (persistent) table, where the regular table exists permanently in your database until you explicitly drop it.
What is @@SERVICENAME in SQL Server?
In SQL Server, the @@SERVICENAME configuration function returns the name of the registry key under which SQL Server is running.
No argument is required. You can simply use it in a SELECT statement to return the registry key’s name.
Note that SQL Server runs as a service named MSSQLServer. The @@SERVICENAME function returns MSSQLSERVER if the current instance is the default instance. It returns the instance name if the current instance is a named instance.
Introduction to User-Defined Functions in SQL Server
SQL Server ships with a collection of built-in functions that enable you to perform a variety of operations. Each built-in function serves a specific purpose, and can’t be modified. If a function serves your purpose, you can go ahead and use it.
But what if you can’t find a function that serves your purpose?
Then it’s time to write your own user-defined function.
What is a Scalar UDF in SQL Server?
In SQL Server, a scalar UDF, or scalar user-defined function, is a user-defined function that returns a single value.
This is in contrast to a table-valued function, which returns a result set in the form of a table.
User-defined functions can be written as either T-SQL UDFs or CLR (Common Language Runtime) UDFs. CLR enables you to create UDFs in managed code using any .NET Framework programming language. These functions are then accessible to T-SQL or other managed code.
What is a Table-Valued Function in SQL Server?
In SQL Server, a table-valued function (TVF) is a user-defined function that returns a table. This is in contrast to a scalar function, which returns a single value.
You can invoke a table-valued function in the same way that you can query a table. For example, you can use it in a SELECT statement. In some cases, table-valued functions can also be used to update, delete, and insert data.
What is a Computed Column in SQL Server?
In SQL Server, a computed column is a virtual column that uses an expression to calculate its value.
A computed column will typically use data from other columns in its calculation. If data in any of those columns is updated, the computed column will automatically reflect the update in its calculation.
What is @@MAX_PRECISION in SQL Server?
In SQL Server, the @@MAX_PRECISION configuration function returns the precision level used by decimal and numeric data types as currently set in the server.
No argument is required. You can simply use it in a SELECT statement to return the precision level of the current server.
What is @@TEXTSIZE in SQL Server?
In SQL Server, the @@TEXTSIZE configuration function returns the current value of the TEXTSIZE option.
No argument is required. You can simply use it in a SELECT statement to return the current TEXTSIZE value.
The TEXTSIZE value specifies the size of varchar(max), nvarchar(max), varbinary(max), text, ntext, and image data returned by a SELECT statement. This value can be set using SET TEXTSIZE.