PostgreSQL重用函数调用结果

Question

我想在PostgreSQL中重用一个昂贵的函数调用：

SELECT name,
  expensive_function(bar) as bars,
  array_length(bars) as total
FROM foos
GROUP BY name

但当然bars不是列，因此会引发以下错误：

ERROR:  column "bars" does not exist

是否有一种语法或技巧可以使其发挥作用？

Answer 1

公用表表达式（CTE）可以工作：

WITH subqry AS
  ( SELECT expensive_function(bar) AS bars
    FROM   foos )
SELECT bars,
       array_length(bars)
FROM   subqry;