The following examples use SQL to delete duplicate rows that have a primary key or unique identifier column.
Specifically, the examples delete all duplicates except one. So for example, in the case of three identical rows, it deletes two of them and keeps one.
Continue readingHere are examples of using SQL to return rows that contain non-alphanumeric characters in various DBMSs.
Non-alphanumeric characters include punctuation characters like !@#&()–[{}]:;',?/* and symbols like `~$^+=<>“, as well as whitespace characters like the space or tab characters.
If you ever need to use SQL to return just the numeric values in a character column, the method you use will largely depend on your DBMS. Most DBMSs support regular expressions (regex), but some don’t. And some include functions that can detect numeric values.
Here are examples of how to do it in the more popular DBMSs.
Continue readingMost RDBMSs provide at least a few ways to return rows that contain uppercase characters. Here are some options available in the major RDBMSs.
Continue readingBelow 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.
Continue readingThe SQL Server CASE statement evaluates a list of conditions and returns one of multiple possible result expressions.
Although it’s commonly known as the “CASE statement”, the SQL Server documentation lists it as an expression. Plus it’s referred to as the “CASE expression” in the SQL standard. Some other DBMSs distinguish between the CASE statement and the CASE expression. Either way, here’s a quick rundown on how the “CASE statement” (or CASE expression) works in SQL Server.
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.
Continue readingMost RDBMSs provide at least a few ways to return rows that contain lowercase characters. Here are some options available in the major RDBMSs.
Continue readingHere’s an example of using SQL to find duplicate rows in a database table. This technique can be used in most of the major RDBMSs, including SQL Server, Oracle, MySQL, MariaDB, PostgreSQL, and SQLite.
Continue readingHere are examples of converting a Unix timestamp to a date/time value in some of the major RDBMSs.
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 reading