Database Management Systems
Below are two options for finding those rows that only contain non-alphanumeric characters in MySQL.
Non-alphanumeric characters include punctuation characters like !@#&()–[{}]:;',?/* and symbols like `~$^+=<>“, as well as whitespace characters like the space or tab characters.
In PostgreSQL, we can use the + operator to add one or more hours to a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also add hours to a date value or a date and time combination.
If you’re getting “Error: in prepare, SELECTs to the left and right of UNION do not have the same number of result columns…” in when trying to use the UNION operator in SQLite, it’s because one of the SELECT statements is returning more columns than the other.
If you need to calculate the number of seconds that have passed since a given date and time, you can use the UNIXEPOCH() function.
Note that this function was introduced in SQLite 3.38.0, so it will only work if you’re using SQLite 3.38.0 or later.
Continue readingIn PostgreSQL, we can use the initcap() function to format a string of text to use initial capitals. That is, it converts the first letter of each word to upper case and the rest to lower case.
Here are a couple of ways to show a list of databases when using psql with PostgreSQL.
The first option can be used when we’re already connected to PostgreSQL. The second option can be used when we don’t currently have a connection to Postgres.
Continue readingIn SQLite, we can use the DATE() function to add a given number of days to a date.
If we’re dealing with datetime values, we can use the DATETIME() function.
When using the SQLite command line interface (CLI), by default, whenever a query returns a null value, the output is the empty string ('').
We can change this by using the -nullvalue command line option when launching SQLite.
We can also use the .nullvalue dot command if we’re already in the SQLite CLI.
In MariaDB, we can use the UPPER() function to convert lowercase characters to their uppercase equivalent.
We can alternatively use UCASE(), which is a synonym of UPPER().
Below is a full list of JSON functions and JSON operators available in SQLite.
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