MySQL CTE递归查询 Data too long for colum‘xxx‘ at row 1

在mysql 8 使用 CTE递归查询时，出现了这个报错

WITH recursive area AS (
 SELECT
 area_name, 
 area_code
 FROM
 sys_area_tree
 WHERE
 area_category = '1'
 AND parent_code IS NULL UNION ALL
 SELECT
 concat( t1.area_name, '/', t.area_name ),
 t.area_code
 FROM
 sys_area_tree t
 INNER JOIN area t1 ON t.parent_code = t1.area_code
 AND t.area_category = '1'
) 
select * from  area

原因：

是因为参与递归concat的【area_name】字段超出了长度限制，也就是说在非递归语句中，一开始【area_name】字段的长度就确定了

解决方案：

在cte表达式中非递归的查询语句中，将初始字段的长度重新转换一下，cast(xxx as CHAR(1024)) area_name

将sql 修改为：

WITH recursive area AS (
SELECT
cast( area_name AS CHAR ( 1024 )) area_name,
area_code
FROM
sys_area_tree
WHERE
area_category = '1'
AND parent_code IS NULL UNION ALL
SELECT
concat( t1.area_name, '/', t.area_name ),
t.area_code
FROM
sys_area_tree t
INNER JOIN area t1 ON t.parent_code = t1.area_code
AND t.area_category = '1') 
select * from area

参考：https://dev.mysql.com/doc/refman/8.0/en/with.html