Object-Relational

How to Create a Generated Column in Oracle

June 24, 2022 by Ian

Oracle Database supports the creation of generated columns. A generated column is a column whose value is derived from an expression that computes values from other columns.

In Oracle Database, generated columns are usually referred to as virtual columns. Generated columns can also be referred to as computed columns in other RDBMSs (such as SQL Server). Either way, they do pretty much the same thing – they contain an expression that computes a value based on values in other columns in the same table.

Find Rows that Contain Uppercase Characters in SQL

June 22, 2022 by Ian

Most RDBMSs provide at least a few ways to return rows that contain uppercase characters. Here are some options available in the major RDBMSs.

How to Get the First Day of the Month in Oracle

June 20, 2022 by Ian

Here’s an example of returning the first day of a given month in Oracle Database. We can return the first day of the current month, a previous or later month, or the first day of a month based on a specified date.

How to Get the Last Day of the Month in SQL

November 7, 2025June 15, 2022 by Ian

Below are examples of using SQL to return the last day of the month across various DBMSs.

This could be the last day of the current month, or the last day of a month based on a given date.

SQL NVL2() Explained

June 9, 2022 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).

SQL NVL() Explained

June 8, 2022June 8, 2022 by Ian

Some DBMSs provide an NVL() function, which can be used when working with potentially NULL values. The function allows us to replace any NULL values with another value.

Find Duplicate Rows that have a Primary Key in SQL

October 13, 2023June 7, 2022 by Ian

Here are examples of using SQL to return duplicate rows when those rows have a primary key or other unique identifier column.

These queries work in most of the major RDBMSs, including SQL Server, Oracle, MySQL, MariaDB, PostgreSQL, and SQLite.

How to Get the Definition of a Generated Column in PostgreSQL

June 6, 2022 by Ian

If you have a generated column in PostgreSQL, you can use the following methods to find the definition of that column.

Find Rows that Contain Lowercase Characters in SQL

June 4, 2022 by Ian

Most RDBMSs provide at least a few ways to return rows that contain lowercase characters. Here are some options available in the major RDBMSs.

Oracle CASE Statement

June 3, 2022 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.