FIFO type Recently Viewed Pages - php

Question

I would like to create 20 rows of table data for to store recently viewed pages. The table row should not increase above 20 rows.
For an example, first 20 rows of page id with title will be stored in that table. when the 21st page viewed by the user, then the first post id and post title will be deleted (i.e., first viewed post) and insert (i.e., last viewed post) in the same table.
my table format:
-------------------------------|
ID | Post Title
-------------------------------|
1 | Post Title 1
2 | Post Title 2
3 | Post Title 3
...
20 | Post Title 20
-------------------------------|
if anyone please tell me how to do that with optimized qry.

Answer 1

You have two columns id and title. Let's consider that id will have any value even more than 20. At any time this table will contain maximums 20 rows (as per your need).
Understand following terms:
min(id) // will give minimum value in column id
max(id) // will give maximum value in column id
count(id) // counts total number of rows of your table
new_id // id of row which will be inserted next
Algorithm:
if(count(id)<20) // table have less than 20 rows so only insert
new_id = max(id)+1
insert the row with id as 'new_id' and page title
else // table have more than 20 rows so delete and then insert
delete row with id = min(id)
new_id = max(id)+1
insert the row with id as 'new_id' and page title
What above solution propose is if you have less than 20 rows keep on inserting because space is still there to insert. But, when you see that rows are more than or equal to 20 first delete the row with minimum id then insert the new row with maximum id of column by adding one.

Answer 2

You can do the following:
LOCK TABLES mytable;
INSERT INTO mytable (title) VALUES ('newtitle');
DELETE t FROM mytable t WHERE t.id IN (SELECT t2.id FROM (SELECT * FROM mytable) t2 ORDER BY t2.id DESC LIMIT 20,999999999); --Delete from 20 to "end"
UNLOCK TABLES;

Answer 3

First you need to add one column in table like created date
while inserting new record to this table, first check total number of rows in table
If rows count == 20 then write a query to delete one old record. use created_date to find it out...
if row count is < 20 then you can insert record directly...no pre-check required
Above step can be managed in only one query, If you are good at writing query

Answer 4

when user has viewed a page:
$query = mysqli_query("SELECT COUNT(ID) From your-table",$conn);
$result = mysqli_fetch_array($query);
$total = $row[0];
if($total<20){
//INSERT NEW ROW
$query = "INSERT INTO your-table() values(...,...)";
//etc ...
} else{
// DELETE THE FIRST ROW
$query = "DELETE FROM your-table ORDER BY ID ASC LIMIT 1";
// Then insert new row, etc...
}