有三张表
MySQL的写法：group_concat
第一种写法：
select u.name,group_concat(r.name separator \',\') rolesname
from user u left join user_role ur on u.id = ur.user_id
left join role r on ur.role_id = r.id
GROUP BY u.name
第二种写法:
SELECT u.name,group_concat(r.name separator \',\') rolesname
FROM user u , user_role ur, role r
WHERE u.id = ur.user_id
and r.id = ur.role_id
group by u.name;
Oracle的写法：wm_concat
SELECT u.name,to_char(wm_concat(r.name)) rolesname
FROM user u , user_role ur, role r
WHERE u.id = ur.user_id
and r.id = ur.role_id
group by u.name;
当其中一个为主表，其他以主表ID相关联，如
SELECT * FROM
(SELECT A.*, ROWNUM RN FROM
(select om.TKT_USERID,om.ORDER_STATUS,om.PNR_NO,om.RES_OFFICEID,
om.PNR_STATUS,om.PAY_TYPE, op.TKT_FACEFARE,op.TKT_DATE as TKT_DATE,
op.Agent_TotalFare,op.Agent_rate,op.NetFare,op.TaxesBreak,op.Farebasis,
se.ROUTING,se.ORG_TIME,se.BOOKINGCLASS,se.AIRLINE,
op.PASS_NAME,op.Tkt_No,op.Tour_code
FROM ORDER_MAIN om
left join ORDER_PSG op on om.rec_no=op.rec_no
LEFT JOIN (SELECT os.rec_no, wmsys.wm_concat (os.org||os.dest) as ROUTING,
wmsys.wm_concat(to_char(os.ORG_TIME,\'yyyy/MM/dd\'))as ORG_TIME,wm_concat (os.CLASS) AS BOOKINGCLASS,
wmsys.wm_concat(os.AIRLINE) as AIRLINE
FROM order_segment os
where os.seg_status=\'OK\'
GROUP BY os.rec_no
)se ON om.rec_no=se.rec_no
where om.res_userid=\'DL395409\'
and to_date( om.RES_DATE,\'yyyy-mm-dd hh24:mi:ss\')
between to_date(\'2017-12-13 00:00:00\',\'yyyy-mm-dd hh24:mi:ss\') and to_date(\'2017-12-29 23:59:59\',\'yyyy-mm-dd hh24:mi:ss\')
ORDER BY to_date(OM.RES_DATE,\'yyyy-mm-dd hh24:mi:ss\'), OM.ORDER_STATUS
) A WHERE ROWNUM <= \'6\'
) WHERE RN >= \'1\'