2 equals select expression within select

Question

我必须通过 Levenshtein 函数处理我的数据。在这种情况下，我使用嵌套选择

SELECT levenshtein(a.param, b.param), *
FROM   (
         SELECT 5 fields
         FROM table t,
         JOIN x,
         JOIN y,
         GROUP BY 1, 2, 3
       ) a,
FROM   (
         SELECT 5 fields
         FROM table t,
         JOIN x,
         JOIN y,
         GROUP BY 1, 2, 3
       ) b,

有没有办法不重复内部 SELECT？

Answer 1

解决方案非常简单，感谢@Nikarus 对 WITH 表达式的建议：

WITH subtable AS (
    SELECT 5 fields
     FROM table t,
     JOIN x,
     JOIN y,
     GROUP BY 1, 2, 3
)
SELECT levenshtein(a.param, b.param), *
FROM subtable a, subtable b

2 equals select expression within select

2 equals select expression within select

sql

postgresql

postgresql-9.1