大于表达式中的 SQL 多列 [英] SQL multiple columns in greater than expression

问题描述

看到以下与游标分页结果相关的 SQL，但无法找到有关其工作原理的更多信息:

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;

当您在一个比较表达式中有多个列时会发生什么?我还没有找到任何其他的例子.

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

推荐答案

比较是作为元组"从左到右进行的.因此，在每个元组中比较第一个值，然后比较下一个值.所以:

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:

• <代码>(1, 2) >(1, 1) --> 正确
• <代码>(1, 1) >(1, 1) --> 假
• <代码>(2, 1) >(2, 2) --> 假
• <代码>(2, 1) >(1, 10) --> 真

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

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