PostgreSQL allows us to create columns that store arrays. That is, we can define the column as an array column so that we can insert arrays into the column. This enables us to work with the arrays in the columns without it being confused with plain text.
We have a couple of options for inserting arrays into columns. One is to use an array literal. Another is to use an array constructor. Examples of each of these options are below.
Continue readingIf you’re getting SQL Server error 8111 that reads something like “Cannot define PRIMARY KEY constraint on nullable column in table ‘Employees’“, it’s probably because you’re trying to add a PRIMARY KEY constraint to an existing column that is nullable. In other words, the column isn’t defined with a NOT NULL constraint.
We can only add primary keys to columns that are defined as NOT NULL.
To fix this issue, define the table as NOT NULL before attempting to add the primary key.
In SQL, it’s not unusual to see subqueries in SELECT statements, where they can help narrow down the results based on a complex condition.
But the SELECT statement isn’t the only place we can put a subquery.
We can use subqueries in an UPDATE statement, and we can update multiple rows too, if required.
In this article, we look at how to update multiple columns by using a SQL subquery in the UPDATE statement.
When looking at ways to fix slow running SQL queries, one of the first things we might do is look at what indexes are available to support the query. If none are available, then we might look at creating one. And if there is an index, perhaps it doesn’t cater for the query as well as it could.
Indexes are often created on a single column, but this isn’t the only way to create an index. We can also create indexes on multiple columns. These are typically known as composite indexes.
Continue readingWhen it comes to prepending a values to arrays in PostgreSQL, we have a number of options available to us. Below are four methods we can use to prepend a value to an array in PostgreSQL.
Continue readingIf you’re getting SQL Server error Msg 15248 that reads something like “Either the parameter @objname is ambiguous or the claimed @objtype (INDEX) is wrong’“, it appears that you’re trying to perform an operation on an index, but you’ve got the naming syntax slightly wrong. Perhaps you’re trying to rename it.
When we do stuff like rename an index, we need to include the table name when referring to the existing index. It’s possible that you’ve not included this in your code.
To fix this issue, be sure to include the table name.
Continue readingIn SQL Server, a heap is a table without a clustered index. Unlike tables with clustered indexes, which sort data in a specific order, heaps store data in no particular order. That’s because the clustered index is what determines how the table is stored and sorted (it’s sorted on the clustered index’s key column).
If there’s no clustered index, then data is initially stored in the order in which the rows are inserted, although the database engine may change this in order to store the rows more efficiently.
Continue readingJSON (JavaScript Object Notation) has become a ubiquitous data format for storing and exchanging information. SQL Server 2016 and later versions provide robust support for working with JSON data. This article explores some useful tips and tricks for handling JSON in T-SQL.
Continue readingIf you find yourself with an index in SQL Server that you no longer need, you may decide to disable it, or you may opt to get rid of it altogether. That way you can declutter your database, free up space, and perhaps help improve performance of updates to the data.
Typically, to delete an index in SQL Server, we use the DROP INDEX statement. There are cases where we might drop it via other means (for example, if it’s implemented as part of a PRIMARY KEY or UNIQUE constraint – also shown below), but DROP INDEX is usually the go to command for such operations.
If you’re getting SQL Server error 159 that reads “Must specify the table name and index name for the DROP INDEX statement“, it’s probably because you’re trying to drop an index without specifying the table name.
When we drop an index, we must specify both the index name and the table name.
To fix this issue, include both the index name and the table name in your DROP INDEX statement.