Oracle listagg如何去重

原文链接：https://www.cnblogs.com/lgx5/p/17515131.html

1.去重思路：利用listagg会忽略null值的特点

2.上SQL：

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with T_TEST as
(
select 'TOOL-001' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TOOL-003' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual union all
select 'TOOL-001' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TOOL-003' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 123456 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual
)
select t.entity_group_rrn,
listagg(decode(rne, 1, t.eqpt_id, null), ',') within group(order by t.eqpt_id) eqpt_ids,
listagg(decode(rns, 1, t.station_id, null), ',') within group(order by t.station_id) station_ids
from (select row_number() over(partition by t.entity_group_rrn,t.eqpt_id order by rownum) rne,
row_number() over(partition by t.entity_group_rrn,t.station_id order by rownum) rns,
t.*
from T_TEST t) t
group by t.entity_group_rrn;
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查询结果

总结
1、通常情况可以先分组去重，再合并即可，除非遇到同一分组中，多列分别有重复值，才需要上面那样处理
2、还有另一种去重办法，使用 wm_concat + distinct ，如下：

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with T_TEST as
(select 'TOOL-001' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TOOL-003' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'JITAI-1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S1' STATION_ID from dual union all
select 'TEST2' EQPT_ID, 10493721 ENTITY_GROUP_RRN, 'S2' STATION_ID from dual
)
select wm_concat(distinct t.EQPT_ID) ids,entity_group_rrn, wm_concat(distinct t.station_id) ids2
from T_TEST t group by t.entity_group_rrn
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但是由于官方不推荐使用 wm_concat ，所以尽量不要用此方法