Question

我需要找到一种方法来从PostgreSQL的数组中确定最常见的子字符串。

我在PostgreSQL的一列中有一个维数组，用于存储CPV值（嵌套分类词汇-https://simap.ted.europa.eu/cpv）。这些代码由数字字符组成，但是由于某些记录的前导零而存储为varchar，如下所示：

["45331110", "50721000", "45251250", "42160000", "39715000", "45315000", "09323000", "71321200", "45331100", "50720000"]

我想使用PostgreSQL从该数组中提取最常见的前两位数字，在示例情况下为45。

Answer 1

如果您想每行获得最常见的前两位数字，则可以使用：

WITH data_rows(id, cpv_values) AS (
    VALUES (1, ARRAY ['45331110', '50721000', '45251250','42160000','39715000','45315000', '09323000','71321200','45331100', '50720000'])
         , (2, ARRAY ['50721000']) -- second test case
)
SELECT id, leading_two_digits
FROM data_rows
-- for every row in `data_rows` (your table),
-- select the most common `leading_two_digits` (through GROUP BY/ORDER BY/LIMIT 1)
JOIN LATERAL (
    SELECT left(code, 2) AS leading_two_digits
    FROM unnest(cpv_values) AS f(code)
    GROUP BY left(code, 2)
    ORDER BY COUNT(*) DESC
    LIMIT 1
) s ON true

返回

+--+------------------+
|id|leading_two_digits|
+--+------------------+
|1 |45                |
|2 |50                |
+--+------------------+

如果要在所有行中使用最常见的前两位数字，则可以使用：

WITH data_rows(cpv_values) AS (
    VALUES (ARRAY ['45331110', '50721000', '45251250','42160000','39715000','45315000', '09323000','71321200','45331100', '50720000']),
           (ARRAY ['45'])
)
SELECT left(code, 2) AS leading_two_digits
FROM data_rows, unnest(cpv_values) AS f(code)
GROUP BY left(code, 2)
ORDER BY COUNT(*) DESC
LIMIT 1

Answer 2

此查询可满足您的需求。

select substr(t, 1, 2) mc
 from unnest(array['45331110', '50721000', '45251250', '42160000', '39715000', '45315000', '09323000', '71321200', '45331100', '50720000']) t 
 group by mc
 order by count(1) desc
 limit 1;

结果：

Name|Value|
----|-----|
mc  |45   |

您可以使用上面的thie作为子查询来提取每行最常见的子字符串。

PostgreSQL-在数组中查找最常见的substring（）

2 个答案: