mysql GROUP_CONCAT 활용 및 max 사이즈 변경

1. max 사이즈 조회

SELECT @@group_concat_max_len

2. max 사이즈 변경

SET @@group_concat_max_len = 1000000;

예) 

SELECT a.vehicle_seq

, a.license_plate

, GROUP_CONCAT(a.start_date ORDER BY a.start_date) start_date

, GROUP_CONCAT(a.result_value ORDER BY a.start_date) result_value

, LENGTH(GROUP_CONCAT(a.start_date ORDER BY a.start_date)) start_date_length

, LENGTH(GROUP_CONCAT(a.result_value ORDER BY a.start_date)) result_value_length

FROM (

SELECT d.vehicle_seq

, (SELECT v.license_plate FROM vehicle v WHERE d.vehicle_seq = v.vehicle_seq) license_plate

, DATE_FORMAT(d.start_date, '%Y-%m-%d %H:%i') start_date

, d.result_value

FROM dvr_position d

GROUP BY d.vehicle_seq, DATE_FORMAT(d.start_date, '%Y%m%d%H%i')

) a

GROUP BY a.license_plate;

결과 )