tidb: add some simple select benchmark.
tidb: add some simple select benchmark.

yuanwhy/tidb,andelf/tidb,yangwenmai/tidb,Nify/tidb,XuHuaiyu/tidb,JinheLin/tidb,Cofyc/tidb,c4pt0r/tidb,andelf/tidb,liyu4/tidb,gaocegege/tidb,simon-xia/tidb,tiancaiamao/tidb,kyle-wang/tidb,anywhy/tidb,zimulala/tidb,kyle-wang/tidb,ngaut/tidb,Cofyc/tidb,qiuyesuifeng/tidb,ngaut/tidb,pingcap/tidb,wusphinx/tidb,silentred/tidb,qhsong/tidb,mccxj/tidb,myrice/tidb,pingcap/tidb,louishust/tidb,zimulala/tidb,silentred/tidb,kyle-wang/tidb,gaocegege/tidb,ueizhou/tidb,yangwenmai/tidb,qhsong/tidb,coocood/tidb,ngaut/tidb,cosmtrek/tidb,silenceper/tidb,silenceper/tidb,wusphinx/tidb,spongedu/tidb,liyu4/tidb,c4pt0r/tidb,8cbx/tidb,ngaut/tidb,CodeRushing/tidb,astaxie/tidb,c4pt0r/tidb,pingcap/tidb,simon-xia/tidb,ming-relax/tidb,Nify/tidb,pingcap/tidb,ngaut/tidb,JinheLin/tidb,ueizhou/tidb,qiuyesuifeng/tidb,zs634134578/tidb,spongedu/tidb,myrice/tidb,EvilMcJerkface/tidb,kyle-wang/tidb,kyle-wang/tidb,c4pt0r/tidb,astaxie/tidb,pingcap/tidb,pingcap/tidb,louishust/tidb,CodeRushing/tidb,yuanwhy/tidb,ming-relax/tidb,XuHuaiyu/tidb,ngaut/tidb,EvilMcJerkface/tidb,c4pt0r/tidb,anywhy/tidb,mccxj/tidb,kyle-wang/tidb,tiancaiamao/tidb,zs634134578/tidb,c4pt0r/tidb,8cbx/tidb,cosmtrek/tidb,coocood/tidb