If you’re getting SQL Server error 1785 that reads something like “Introducing FOREIGN KEY constraint ‘FK__Name’ on table ‘Department’ may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints“, it’s probably because you’ve specified the CASCADE option when trying to create a foreign key with a circular reference, or one that has multiple cascade paths (perhaps your child table has multiple foreign keys to the same primary key on the parent table).
Author: Ian
What is Domain Integrity?
Domain integrity is an important concept in relational database management that ensures the accuracy, validity, and consistency of data within a database. It refers to the enforcement of rules and constraints that ensure data entered into a database adheres to a predefined set of acceptable values. This helps maintain the quality of data and prevents the entry of erroneous, incomplete, or invalid data into the system.
Continue readingEnlarging an Array in PostgreSQL
In PostgreSQL it’s possible to make an array larger without providing any values. For example, we can take an array with three elements, and enlarge it so that it contains say, five elements, with the two extra elements being NULL.
We can also do it so that some of the extra elements are non-NULL and others are NULL.
Fix Error 1989 “Cannot enable foreign key constraint … as index … on referenced key is disabled” in SQL Server
If you’re getting SQL Server error 1989 that reads something like “Cannot enable foreign key constraint ‘FK_Jobs_Employees’ as index ‘PK__Employee__7AD04FF1A39ECAB1’ on referenced key is disabled“, it’s probably because you’re trying to enable a foreign key, when the index that it references is disabled.
For example, if you’ve disabled a primary key on the parent table, and then try to enable a foreign key that references that primary key, then you’ll get this error.
To fix this issue, enable the index for the primary key/referenced key before enabling the foreign key.
Continue readingCreate an Index in SQL Server
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.
Using ON DELETE SET NULL for Foreign Keys in SQL Server
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.
Fix Error 2714 “There is already an object named ‘…’ in the database” in SQL Server
If you’re getting SQL Server error 2714 that reads something like “There is already an object named ‘Actors’ in the database” it seems that you’re trying to create an object that already exists.
It could be that you didn’t know that the object had already been created. Or it could be that you’re trying to create a different object, but you’re inadvertently using the same name that another object has. Or it could be that you want both objects to have the same name, but a different schema. In this case, perhaps you inadvertently omitted the schema name from the object.
Continue readingUnderstanding PostgreSQL’s FILTER Clause
When using aggregation functions in PostgreSQL, we have the option of including a FILTER clause. This clause allows us to narrow down – or filter – the rows that are fed to the aggregate function.
This can be be a handy way to provide functionality that we might otherwise need to use a CASE statement or perhaps a CTE.
In this article, we’ll take a look at PostgreSQL’s FILTER clause, and see how it can simplify our SQL queries by replacing CASE statements with more concise code.
What is Entity Integrity?
When working with relational databases, data accuracy and consistency are paramount. When we talk about maintaining the integrity of the data within a relational database, several types of integrity come into play. One of the most fundamental is entity integrity.
This concept is crucial for ensuring that each record within a database table is uniquely identifiable, which in turn supports the reliability of the data. In this article, we will delve into what entity integrity is, why it matters, and how it is implemented in practice. We’ll also look at an example to clarify the concept further.
Continue reading“Incorrect syntax” Error When Creating a Filtered Index in SQL Server due to an Unsupported Operator
If you’re getting the “Incorrect syntax…” error in SQL Server when trying to create a filtered index, it could be that you’re using an unsupported operator.
Filtered indexes in SQL Server only support simple comparison operators. If you use an unsupported operator or expression, you’ll likely get the dreaded “Incorrect syntax” error.
To fix, either use a supported operator, or create a view.
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