How to properly block rows?

Question

MySQL

Greetings!
In general: clients come to the server and take the top line from a certain table according to the time sorting, leaving 1 in the locked field after themselves.
The problem appeared with the increase in load, clients began to receive the same lines.
How can you prevent concurrent retrieval of rows?
I've only heard of blocking, I have a hard time understanding how it works.

Answer 1

In theory, this is how it should work. I don’t know what syntax you use, so I only give commands:

LOCK TABLES my_table WRITE;
SELECT * FROM my_table;
UNLOCK TABLES;

Answer 2

I had the same problem, it works like this for me:

// Заблокировать и читать
    mysqli_query($link," LOCK TABLES `".$source_table."` WRITE ");
    mysqli_query($link," SELECT `data` FROM `".$source_table."`   LIMIT 1 ");

// Удалить только что прочитанное и разблокировать
    mysqli_query($link," DELETE FROM `".$source_table."` WHERE `id`=".$lastid."");
    mysqli_query($link," UNLOCK TABLES ");