MySQL字符串数据在group_concat中截断并按顺序排序

Question

我有这个SQL工作正常，但截断长度超过1024字节的字符串字段的序列化数据。我试图更改mysql变量group_concat_max_len，但没有任何改变。是否还有其他可能涉及的会话变量？

set session group_concat_max_len = 100000;
SELECT CONCAT(AREA,';',
              COLORE,';',
              CAST(PERCENTUALE AS CHAR(20)),';',
              CAST(TRASPARENZA AS CHAR(20)),';',
              DATE_FORMAT(DATA_MISURA,'%Y%m%d'),';', 
              ( SELECT GROUP_CONCAT( CONCAT( CAST(X AS CHAR(20)), ' ', CAST(Y AS       
                CHAR(20)) ) ORDER BY PROGRESSIVO_VERTICE SEPARATOR ';')
                FROM   plan_poligoni 
                WHERE ID_IMM = PP_GEN.ID_IMM 
                  AND SCHEDA = PP_GEN.SCHEDA 
                  AND PROGRESSIVO = PP_GEN.PROGRESSIVO 
                  AND IF(DATA IS NULL,'',DATA) = IF(PP_GEN.DATA IS NULL,'',PP_GEN.DATA)),'|') 
AS SERIALIZED_POLYGONS
FROM plan_poligoni AS PP_GEN
WHERE SCHEDA=1 
  AND ID_IMM = 1111 
  AND PROGRESSIVO_VERTICE = 1
GROUP BY ID_IMM, SCHEDA, PROGRESSIVO;