In PostgreSQL, we can use the to_timestamp() function to convert a Unix timestamp value to a date/time value.
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 four options for returning rows that contain uppercase characters in MariaDB.
Continue readingBelow are two options for returning rows that only contain non-alphanumeric characters in PostgreSQL.
Non-alphanumeric characters include punctuation characters like !@#&()–[{}]:;',?/* and symbols like `~$^+=<>“, as well as whitespace characters like the space or tab characters.
MySQL has an IFNULL() function that allows us to easily replace NULL values with another value.
Most major DBMSs provide us with a function for replacing null values with another value.
But the name of the function tends to differ across DBMSs. For example, SQL Server has an ISNULL() function, while others (such as MySQL, MariaDB, and SQLite) have an IFNULL() function for doing the same thing.
However, to confuse matters, MySQL and MariaDB each have an ISNULL() function that works differently to SQL Server’s function of the same name (MySQL and MariaDB’s implementation only accept a single argument, and return 1 if its null and 0 if it’s not).
In MySQL, the ISNULL() function enables us to check whether a value is null or not. If it’s null, then 1 is returned, otherwise 0 is returned.
The following SQLite examples return only those rows that have non-numeric values in a given column.
Continue readingWe can use the - operator to subtract one or more weeks from a date in PostgreSQL.
In MariaDB, the IFNULL() function allows us to replace NULL values with another value.
From MariaDB 10.3, NVL() can be used as an alias for the IFNULL() function. Therefore, both functions enable us to replace NULL values with another value.