SELECT DISTINCT with other colum - php

Question

I got a question.
I have following mysql table:
domain | visited
domain1.net | 21.02.2019 - 18:55
domain1.net | 20.02.2019 - 14:01
domain1.net | 22.02.2019 - 12:05
domain2.net | 24.02.2019 - 19:01
domain2.net | 22.02.2019 - 17:21
I want following result:
domain1.net | 22.02.2019 - 12:05
domain2.net | 24.02.2019 - 19:01
No duplicate domain and the latest visited.
My code:
<?php
$sql = "SELECT DISTINCT p_domain FROM table_content";
$result = $db->prepare($sql);
$result->execute();
while ($row = $result->fetch()) {
$domain = $row['domain'];
echo "<tr>"
. "<td>$domain</td>"
. "</tr>";
}
?>

Answer 1

You can use your domain DISTINCT with your column, to get the latest visited domain you can use Order by
SELECT DISTINCT domain FROM table_content Order By visited DESC
ORDER BY: Order by clause is used to sort the data in ascending or descending order.
DISTINCT: The SELECT DISTINCT statement is used to retrieve only distinct (different) values from the database.

Answer 2

You use GROUP BY:
SELECT p_domain, MAX(visited) as most_recent_visit
FROM table_content
GROUP BY p_domain
Group by establishes a list of columns that you want the unique combinations of. Other columns in your select that are not in the group by list do not form a unique grouping key and MUST be expressed as some form of aggregation:
SELECT ethnicity, city, AVG(age), COUNT(*), SUM(number_of_cars_owned), MIN(birthdate), MAX(number_of_children)
FROM person_table
GROUP BY ethnicity, city
This gets the average age, total count, the total of cars owned, the oldest person, the largest family per ethnic group per city
It is important to note that the values for the aggregates come from different rows (in the Chicago Caucasian category, the Smith family might have the most children but the Doe family has the oldest person), and might not be present in the rows at all (the average age might be 27.32615).
A common query is like "I want to find the earliest date someone visited each of my sites and what their ip address was" - that is a site, min(visitdate) group by site but you can't just bang the IP address in there too, either as a grouped thing site, ipaddress min(visitdate) group by site, ipaddress because that is "the first visit per site per ip" and you can't whack the ip into an aggregating function site, min(visitdate), min(ipaddress) group by site because the min ip may come from a different row to the min date.
If you want the site, the first visit date and the ip of that visit you have to run the aggregate as a subquery and join it back to the main table to get the other data from the row with the min date
select *
from
(select site, min(visitdate) min_d from t group by site) x
inner join t on t.site = x.site and t.visitdate = x.min_d
ps: the comment makes a really good point; if your visited date isn't a date but instead a string-that-looks-like-a-date-to-you then getting the MAX() of it will not necessarily return the most recent date, it will return the alphabetically latest date. You should definitely store dates using the proper date/time data types so that functions like MAX can work properly. If you haven't done this please change things so it is done like this.. because writing a query that parses millions of strings into dates every time it is run, just so that max will work properly, is a huge waste of resources.