SQL multiple columns in greater than expression

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Saw the following SQL relating to paging results with cursors and am having trouble finding more information on how part of it works:

SELECT b.* FROM books b
WHERE (b.name, id) > (select b2.name, b2.id
                      from books b2
                      where b2.id = ?
                      )
ORDER BY b.name;

What happens when you have multiple columns within a single comparison expression? I haven't found any other examples of this.

where postgresql pagination sql comparison
1 Answers

The comparisons are made as "tuples", from left to right. So, the first value is compared in each tuple, then the next is compared. So:

  • (1, 2) > (1, 1) --> true
  • (1, 1) > (1, 1) --> false
  • (2, 1) > (2, 2) --> false
  • (2, 1) > (1, 10) --> true
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