If you have a generated column in PostgreSQL, you can use the following methods to find the definition of that column.
Continue readingCategory: DBMS
Database Management Systems
Add Years to a Date in SQLite
In SQLite, we can use the DATE() function to add one or more years to a date.
For datetime values, we can use the DATETIME() function.
Find Rows that Contain Lowercase Characters in SQL
Most RDBMSs provide at least a few ways to return rows that contain lowercase characters. Here are some options available in the major RDBMSs.
Continue readingOracle CASE Statement
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.
How to Create a Generated Column in PostgreSQL
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.
Continue readingSelect Duplicate Rows in SQL
Here’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 reading2 Ways to Get the Definition of a Generated Column in MySQL
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.
Continue readingHow to Convert a Unix Timestamp to a Date/Time in SQL
Here 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 readingSubtract Minutes from a Time Value in SQLite
In SQLite, we can use the TIME() function to subtract one or more minutes from a time value.
For datetime values, we can use the DATETIME() function.
Oracle CASE Expression
In Oracle Database, the CASE expression compares a list of conditions and returns one of multiple possible expressions. It allows us to use IF … THEN … ELSE logic in SQL statements without having to invoke procedures.
The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it.
Oracle also has a CASE statement that’s very similar to the CASE expression, but with some minor differences.