executor, planner: refine merge join compare methods to avoid some rare cases (#9390)#9438

Merged

zz-jason merged 1 commit intopingcap:release-2.1from zz-jason:cherrypick/2.1-mergejoin-compare-funcs

Feb 25, 2019

+310-113

Commits on Feb 25, 2019

executor, planner: refine merge join compare methods to avoid some rare cases (pingcap#9390 )
zz-jason
committed