sql - 有postgres CLOSEST运算子吗？

我在找一张桌子，上面写着：

| id | number |
|  1 |     .7 |
|  2 |   1.25 |
|  3 |   1.01 |
|  4 |    3.0 |

查询SELECT * FROM my_table WHEREnumberCLOSEST(1)将返回第3行。我只关心数字。现在我有一个过程，它只循环遍历每一行并进行比较，但是我认为信息应该可以从b树索引中获得，所以这可能是一个内置的，但是我找不到任何文档表明它是这样做的。

最佳答案

我可能有点不太懂语法，但是这个参数化查询（所有的？以原始问题的“1”为例）应该运行得很快，基本上是2个B树查找（假设数字是索引的）。

SELECT * FROM
(
  (SELECT id, number FROM t WHERE number >= ? ORDER BY number LIMIT 1) AS above
  UNION ALL
  (SELECT id, number FROM t WHERE number < ? ORDER BY number DESC LIMIT 1) as below
)
ORDER BY abs(?-number) LIMIT 1;

对于这个具有~5e5行的表（索引在number上）的查询计划如下所示：

psql => explain select * from (
        (SELECT id, number FROM t WHERE number >= 1 order by number limit 1)
        union all
        (select id, number from t where number < 1 order by number desc limit 1)
) as make_postgresql_happy
order by abs (1 - number)
limit 1;
                                                  QUERY PLAN
--------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.24..0.24 rows=1 width=12)
   ->  Sort  (cost=0.24..0.24 rows=2 width=12)
         Sort Key: (abs((1::double precision - public.t.number)))
         ->  Result  (cost=0.00..0.23 rows=2 width=12)
               ->  Append  (cost=0.00..0.22 rows=2 width=12)
                     ->  Limit  (cost=0.00..0.06 rows=1 width=12)
                           ->  Index Scan using idx_t on t  (cost=0.00..15046.74 rows=255683 width=12)
                                 Index Cond: (number >= 1::double precision)
                     ->  Limit  (cost=0.00..0.14 rows=1 width=12)
                           ->  Index Scan Backward using idx_t on t  (cost=0.00..9053.67 rows=66136 width=12)
                                 Index Cond: (number < 1::double precision)
(11 rows)

关于sql - 有postgres CLOSEST运算子吗？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/6102824/