Author: Ian

SQL NVL2() Explained

Posted on by Ian

Some DBMSs have an NVL2() function that allows us to replace a value with another value, the new value being determined by whether or not the initial value is null.

It’s similar to the NVL() function, except that NVL2() accepts exactly three arguments. This allows us to specify a different value to return in the event the first argument is not null.

In contrast, with the NVL() function, some DBMSs accept only two arguments (which makes the function a synonym for the IFNULL() function) while others accept an unlimited number of arguments (which makes it a synonym for the COALESCE() function).

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Oracle CASE Statement

Posted on by Ian

In Oracle Database, the CASE statement compares a list of conditions and returns one of multiple possible expressions.

Oracle Database’s CASE statement is very similar to the CASE expression (which is defined in the SQL standard (ISO/IEC 9075)). However, Oracle supports both the CASE expression and the CASE statement, and there’s a distinction between the two. The CASE statement can be used to execute of a sequence of PL/SQL statements, whereas the CASE expression returns a single value. Also, there’s a difference in how they deal with the lack of an ELSE clause when a condition is not met.

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How to Create a Generated Column in PostgreSQL

Posted on by Ian

In PostgreSQL, a generated column is a special column that is always computed from other columns. A generated column doesn’t have a fixed value like in a base column. Rather, its value is determined by an expression that references other columns in the table.

Generated columns are included in the SQL standard (ISO/IEC 9075), and are supported by most major RDBMSs. Generated columns were first introduced in PostgreSQL 12.

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2 Ways to Get the Definition of a Generated Column in MySQL

Posted on by Ian

A generated column is one whose value is derived from an expression, as opposed to a fixed value. The expression typically uses other columns in the same table to compute the derived value.

We can create a generated column in MySQL very easily. But what if we want to go back later and see its definition?

Here are two options for returning the definition of a generated column in MySQL.

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