In PostgreSQL, we can use the + operator to add one or more minutes to a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also add minutes to a date value or a date and time combination.
In PostgreSQL, we can use the - operator to subtract one or more seconds from a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also subtract seconds from a date value or a date and time combination.
Below are examples of using SQL to return the first day of the month across various DBMSs.
This could be the first day of the current month, or the first day of a month based on a given date.
Continue readingIn PostgreSQL, we can use the + operator to add one or more seconds to a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also add seconds to a date value or a date and time combination.
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 readingPostgreSQL has supported generated columns since version 12. Generated columns can be created easily with the CREATE TABLE and ALTER TABLE statements.
We can check whether a table contains a generated column or not with the following methods.
Continue readingIn PostgreSQL, the CASE expression 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.
Here 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.
Here are a couple of options for getting a list of tables in a database in PostgreSQL.
The first option is a psql command, the second involves querying an information schema view.
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.
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