postgres通过允许列别名作为 order by 钥匙。所以这是可行的：

SELECT  CONCAT(first_name, last_name)  AS full_name
FROM customer
ORDER BY full_name;

但是，它不会将此扩展到使用别名的表达式。您可以使用子查询或CTE修复此问题。我也可以建议横向连接：

SELECT v.full_name
FROM customer c CROSS JOIN LATERAL
     (VALUES (CONCAT(c.first_name, c.last_name))) v(full_name)
ORDER BY v.full_name;

你能试试下面的一种吗？

SELECT  concat(first_name,last_name) COLLATE "C"  AS full_name from customer
ORDER BY  length(full_name)

或

SELECT  concat(first_name,last_name)  from customer
ORDER BY  length(concat(first_name,last_name))

这将起作用，并避免重复使用 concat() ```
WITH results AS (
SELECT concat(first_name, last_name) AS full_name FROM customer
)
SELECT full_name FROM results ORDER BY length(full_name)