In SQL Server, the FOR XML clause allows us to return the results of a query as an XML document.
When we use this clause, we have various options for how we want to shape the resulting XML document.
Below is an explanation of how the FOR XML clause works, including the basic options we have when using it.
In PostgreSQL, the currval() function returns the value most recently returned by nextval() for the specified sequence in the current session.
The currval() function is very similar to the lastval() function, except that lastval() doesn’t require the name of a sequence like currval() does. That’s because lastval() doesn’t report on any particular sequence – it reports on the last time nextval() was used in the current session, regardless of which sequence was used. The currval() on the other hand, only reports on the specified sequence.
In PostgreSQL, the lastval() function returns the value most recently returned by nextval() in the current session.
The lastval() function is very similar to the currval() function, except that lastval() doesn’t require the name of a sequence like currval() does. That’s because lastval() doesn’t report on any particular sequence – it reports on the last time nextval() was used in the current session, regardless of which sequence was used.
In PostgreSQL, the nextval() function is used to advance sequence objects to their next value and return that value. We pass the name of the sequence when we call the function. This assumes that the sequence object exists.
SQL Server provides us with both a @@ROWCOUNT and a ROWCOUNT_BIG() function. You may be wondering what the difference is between these two functions?
Let’s find out.
In MySQL, BENCHMARK() is a built-in function that executes an expression repeatedly for a specified number of times.
It can be used to time how quickly MySQL processes the expression. Specifically, the function is intended for measuring the runtime performance of scalar expressions.
The result is always 0, or NULL for inappropriate arguments. The function is intended to be used within the mysql command line tool, which reports query execution times.
In the world of database management systems (DBMSs) and computer programming, CRUD is an acronym that stands for Create, Read, Update, and Delete. These are considered to be the four basic operations of persistent storage.
Let’s take a look at how CRUD fits into database management systems and programming in general.
In MySQL and MariaDB we can use the AUTO_INCREMENT keyword to create an automatically incrementing column in a table. In SQLite, we’d use the AUTOINCREMENT keyword. And in SQL Server we can use the IDENTITY property. Some of those DBMSs also allow us to create sequence objects, which provide us with more options for creating an auto-increment type column.
When it comes to PostgreSQL, there are a few ways to create an auto-incrementing column. Below are three options for creating an AUTO_INCREMENT style column in Postgres.
In MySQL, COLLATION() is a built in function that returns the collation of its string argument.
We provide the string when we call the function.
In MySQL, CHARSET() is a built in function that returns the character set of its string argument.
We provide the string when we call the function.