executor: fix group_concat for cases like group_concat(123,null) (#9921)#9930

Merged

zimulala merged 2 commits intopingcap:release-2.1from XuHuaiyu:release-2.1

Mar 28, 2019

+18-16

Commits on Mar 28, 2019

executor: fix group_concat for cases like group_concat(123,null) (pingcap#9921 )
XuHuaiyu
committed
Merge branch 'release-2.1' of https://github.com/pingcap/tidb into release-2.1
XuHuaiyu
committed