mysqlmysql-variables

What's the difference two tables side by side and join tables?

I am looking into the following sql codes, trying to understand but confused:

What does the query actually do when we put the two tables together? What's the difference between this and joining the two tables? Thanks!

select * from
        Logs, (select @count:=0,@record:=(SELECT num from Logs limit 0,1)) r

The Logs table looks like this:

+----+-----+
| Id | Num |
+----+-----+
| 1  |  1  |
| 2  |  1  |
| 3  |  1  |
| 4  |  2  |
| 5  |  1  |
| 6  |  2  |
| 7  |  2  |
+----+-----+
Solution

  • If you don't join the tables, they work like cross join. Number of rows left side * number of rows right side.

    See this.