Below are two options for removing duplicate rows from a table in PostgreSQL when those rows have a primary key or unique identifier column. The primary key is used in the query, but it’s ignored when comparing duplicates (due to the fact that primary keys prevent duplicate rows by definition).
The following examples delete duplicate rows but keep one. So in the case of say, three identical rows, it deletes two and keeps one.
Continue readingIn PostgreSQL, we can use the - operator to subtract one or more hours from a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also subtract hours from a date value or a date and time combination.
Below are two Oracle Database functions that convert uppercase characters to their lowercase equivalent.
Continue readingIn MySQL, the CASE operator compares a list of conditions and returns one of multiple possible result expressions.
The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it.
MySQL also has the CASE statement, which is slightly different to the CASE operator. This article is about the CASE operator.
Here are four options for returning rows that contain lowercase characters in PostgreSQL.
Continue readingIn MariaDB, we can use the CASE operator to compare a list of conditions and return a different result depending on which condition (if any) is matched.
The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it.
MariaDB also has the CASE statement, which is slightly different to the CASE operator. This article is about the CASE operator.
Below are examples of using some of the more popular RDBMSs to return the Unix timestamp.
The Unix timestamp (also known as Unix Epoch time, Unix time, or POSIX time) is the number of seconds that have elapsed since 00:00:00 Thursday, 1 January 1970, Coordinated Universal Time (UTC).
Continue readingHere are two options for returning the number of days in a given month in SQLite. This could be the number of days in the current month, or it could be based on a given date.
Continue readingSome RDBMSs provide an IFNULL() function that can be used when dealing with potentially null values. In particular, MySQL, MariaDB, and SQLite each have an IFNULL() function that replaces any null values with another value.
Other RDBMSs, such as SQL Server, Oracle, and PostgreSQL provide similar functionality via functions of a different name.
Continue readingIn MariaDB, the ISNULL() function checks whether an expression is null or not. If the expression resolves to null, then ISNULL() returns 1, otherwise it returns 0.