Indexes play an important role in SQL database performance. We can use them to speed up commonly run queries, so that users don’t have to sit and wait for their results to come in.
In SQL Server, indexes can be created in several different situations. For example, when we create a primary key or a UNIQUE constraint, an index is created behind the scenes for us. However, we can also create indexes explicitly using the CREATE INDEX statement.
When creating a foreign key constraint in SQL Server, we have the option of including ON DELETE SET NULL in the definition. When we use this option in a foreign key, it tells SQL Server to automatically set the foreign key column values to NULL in the child table when the corresponding primary key record in the parent table is deleted.
Transact-SQL (T-SQL) offers a nice set of functions and methods for manipulating strings. Let’s look at some handy techniques that can help us work more efficiently with string data in SQL Server.
Continue readingTemporal tables can be a powerful way to track historical data changes over time in our SQL Server databases. When we’re working with a database that uses temporal tables, we may need to identify all such tables quickly. Or we may simply want to check to see if it has any temporal tables.
Either way, the following SQL queries can be used to return a list of all temporal tables in the database.
Continue readingWhen working with relational databases, it’s common to encounter situations where you need to delete data from both parent and child tables that are linked by foreign key relationships. This article explores two methods for accomplishing this task in SQL Server, providing detailed examples and explanations for each approach.
Continue readingBy default, if we try to delete a row in the parent table of a referential relationship in SQL Server, we’ll get an error. That’s because the default action is NO ACTION. This means that the delete doesn’t happen, and an error is raised.
But we’re not quite doomed yet. We can use the ON DELETE CASCADE option to ensure that the delete operation does happen, and that no error is returned. This option automatically deletes related records in the child table when a record in the parent table is deleted.
If we’re going to use this option, we need to define it when creating the foreign key. That’s because ON DELETE CASCADE is an optional argument that we can provide when creating the foreign key.
If you’re getting SQL Server error 1988 that reads something like “Cannot rebuild clustered index ‘PK__Employee__7AD04FF1A39ECAB1’ online because it is disabled.“, it’s probably because you’re trying to rebuild a disabled clustered index online.
We can’t rebuild a disabled clustered index with (ONLINE = ON).
In SQL Server, a filtered index is a special type of index that only includes a subset of rows from a table or view, based on specified filter criteria.
This criteria would match the criteria of some of the most commonly run queries on the table, thereby helping to improve the performance of those queries.
Below is an example of creating a filtered index in SQL Server.
Continue readingIf you’re getting SQL Server error Msg 129 that reads “Fillfactor 0 is not a valid percentage; fillfactor must be between 1 and 100“, it appears that you’re trying to set the fillfactor of an index to zero.
While it’s true that zero is the default setting, we can’t actually explicitly set the fillfactor to zero when creating or rebuilding an index.
But all is not lost. Below are two solutions to this problem.
Continue readingIf you’ve got a primary key in SQL Server that you need to enable, you’ll need to enable its index. The index is how we enable and disable primary key constraints in SQL Server.
More specifically, we enable a primary key index (and other indexes) by rebuilding them.
Below is an example of enabling a primary key in SQL Server.
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