Question

When I write below query, it returns all time different sets.

SELECT title, content FROM Stack 
INNER JOIN Overflow ON Stack.OverflowId = Overflow.Id 

For example;

desired result:

title    content
_____    _______
 a     -    c1
 b     -    c2
 c     -    c3
 d     -    c4
 e     -    c5
 f     -    c6
 g     -    c7

First run:

title    content
_____    _______
 g     -    c7
 d     -    c4
 c     -    c3
 b     -    c2
 f     -    c6
 e     -    c5
 a     -    c1

Second run:

title    content 
_____    _______
 d     -    c4
 a     -    c1
 f     -    c6
 b     -    c2
 g     -    c7
 e     -    c5
 c     -    c3

This is reality interesting for me..
Do you know the reason?

When I use below query it is OK.

SELECT title, content FROM Stack 
INNER JOIN Overflow ON Stack.OverflowId = Overflow.Id 
ORDER BY Stack.Id

But the question is

Why do I need ORDER BY to get desired result?

Answer 1

You cannot expect predictable order without ORDER BY. Without it you do not have control over in which order rows are returned. Reason lies in how SQL language is specified.