Python docstring update for sql.py.
Python docstring update for sql.py.

Mostly related to the following two rules in PEP8 and PEP257:
- Line length < 72 chars.
- First line should be a concise description of the function/class.

Author: Reynold Xin <rxin@apache.org>

Closes #869 from rxin/docstring-schemardd and squashes the following commits:

7cf0cbc [Reynold Xin] Updated sql.py for pep8 docstring.
0a4aef9 [Reynold Xin] Merge branch 'master' into docstring-schemardd
6678937 [Reynold Xin] Python docstring update for sql.py.

joseph-torres/spark,jianran/spark,adrian-ionescu/apache-spark,highfei2011/spark,vinodkc/spark,BryanCutler/spark,jrshust/spark,WindCanDie/spark,Aegeaner/spark,lxsmnv/spark,WindCanDie/spark,ericvandenbergfb/spark,wangmiao1981/spark,WeichenXu123/spark,zhouyejoe/spark,mike0sv/spark,Aegeaner/spark,nilsgrabbert/spark,highfei2011/spark,zuotingbing/spark,UndeadBaneGitHub/spark,kimoonkim/spark,esi-mineset/spark,akopich/spark,metamx/spark,bdrillard/spark,huang1900/spark,jiangxb1987/spark,cin/spark,techaddict/spark,stanzhai/spark,rezasafi/spark,gioenn/xSpark,panfengfeng/spark,gengliangwang/spark,xuanyuanking/spark,shaneknapp/spark,debugger87/spark,shubhamchopra/spark,wangyum/spark,akopich/spark,dhruve/spark,bOOm-X/spark,spark-test/spark,goldmedal/spark,loneknightpy/spark,ueshin/apache-spark,zero323/spark,patrick-nicholson/spark,gengliangwang/spark,patrick-nicholson/spark,adrian-ionescu/apache-spark,ajaysaini725/spark,jkbradley/spark,mdespriee/spark,holdenk/spark,lvdongr/spark,panfengfeng/spark,goldmedal/spark,Panos-Bletsos/spark-cost-model-optimizer,SHASHANKB/spark,rikima/spark,bravo-zhang/spark,wangmiao1981/spark,darionyaphet/spark,pronix/spark,aosagie/spark,milliman/spark,jkbradley/spark,narahari92/spark,loneknightpy/spark,haowu80s/spark,ptkool/spark,markhamstra/spark,metamx/spark,rekhajoshm/spark,saltstar/spark,saltstar/spark,1haodian/spark,srowen/spark,witgo/spark,dhruve/spark,goldmedal/spark,BryanCutler/spark,mike0sv/spark,MLnick/spark,rikima/spark,bdrillard/spark,bravo-zhang/spark,byakuinss/spark,MLnick/spark,holdenk/spark,saturday-shi/spark,akopich/spark,zero323/spark,LantaoJin/spark,srowen/spark,ConeyLiu/spark,szhem/spark,jlopezmalla/spark,kevinyu98/spark,joseph-torres/spark,stanzhai/spark,sahilTakiar/spark,liutang123/spark,ioana-delaney/spark,bdrillard/spark,apache/spark,metamx/spark,WeichenXu123/spark,cloud-fan/spark,tejasapatil/spark,mdespriee/spark,facaiy/spark,publicRoman/spark,ericvandenbergfb/spark,vinodkc/spark,apache-spark-on-k8s/spark,gioenn/xSpark,ron8hu/spark,rezasafi/spark,patrick-nicholson/spark,joseph-torres/spark,apache-spark-on-k8s/spark,MLnick/spark,jlopezmalla/spark,kiszk/spark,actuaryzhang/spark,techaddict/spark,cin/spark,ahnqirage/spark,mzl9039/spark,someorz/spark,facaiy/spark,eyalfa/spark,highfei2011/spark,rednaxelafx/apache-spark,haowu80s/spark,apache-spark-on-k8s/spark,rekhajoshm/spark,ueshin/apache-spark,icexelloss/spark,goldmedal/spark,wzhfy/spark,hhbyyh/spark,wangmiao1981/spark,lvdongr/spark,markhamstra/spark,liyichao/spark,ibm-research-ireland/sparkoscope,ericvandenbergfb/spark,patrick-nicholson/spark,actuaryzhang/spark,shuangshuangwang/spark,rekhajoshm/spark,hhbyyh/spark,zzcclp/spark,xuanyuanking/spark,dongjoon-hyun/spark,milliman/spark,ericvandenbergfb/spark,xflin/spark,narahari92/spark,loneknightpy/spark,vinodkc/spark,aokolnychyi/spark,ueshin/apache-spark,jrshust/spark,sachintyagi22/spark,mahak/spark,loneknightpy/spark,mahak/spark,apache/spark,wzhfy/spark,zero323/spark,spark-test/spark,sureshthalamati/spark,gengliangwang/spark,joseph-torres/spark,UndeadBaneGitHub/spark,szhem/spark,zero323/spark,zhouyejoe/spark,JerryLead/spark,andrewor14/spark,byakuinss/spark,sahilTakiar/spark,hhbyyh/spark,rednaxelafx/apache-spark,ericvandenbergfb/spark,mahak/spark,lvdongr/spark,sachintyagi22/spark,witgo/spark,alunarbeach/spark,srowen/spark,pgandhi999/spark,zzcclp/spark,lvdongr/spark,dhruve/spark,aray/spark,ioana-delaney/spark,skonto/spark,byakuinss/spark,ahnqirage/spark,ajaysaini725/spark,Panos-Bletsos/spark-cost-model-optimizer,panfengfeng/spark,SHASHANKB/spark,rikima/spark,ddna1021/spark,mzl9039/spark,srowen/spark,akopich/spark,szhem/spark,1haodian/spark,tejasapatil/spark,andrewor14/spark,jlopezmalla/spark,aray/spark,dongjoon-hyun/spark,mike0sv/spark,WeichenXu123/spark,eyalfa/spark,gioenn/xSpark,nilsgrabbert/spark,someorz/spark,nlalevee/spark,ueshin/apache-spark,kevinyu98/spark,big-pegasus/spark,big-pegasus/spark,yanboliang/spark,kiszk/spark,kissmetrics/spark,SHASHANKB/spark,jkbradley/spark,kimoonkim/spark,cloud-fan/spark,caneGuy/spark,UndeadBaneGitHub/spark,caneGuy/spark,SHASHANKB/spark,zzcclp/spark,ddna1021/spark,guoxiaolongzte/spark,byakuinss/spark,kiszk/spark,rezasafi/spark,aosagie/spark,publicRoman/spark,adrian-ionescu/apache-spark,bOOm-X/spark,andrewor14/spark,poffuomo/spark,narahari92/spark,rikima/spark,skonto/spark,janewangfb/spark,goldmedal/spark,maropu/spark,andrewor14/iolap,HyukjinKwon/spark,saturday-shi/spark,setjet/spark,sahilTakiar/spark,andrewor14/spark,poffuomo/spark,matthewfranglen/spark,andrewor14/iolap,bravo-zhang/spark,markhamstra/spark,gioenn/xSpark,nlalevee/spark,alunarbeach/spark,ConeyLiu/spark,big-pegasus/spark,apache/spark,liutang123/spark,ajaysaini725/spark,darionyaphet/spark,mike0sv/spark,kevinyu98/spark,LantaoJin/spark,ddna1021/spark,LantaoJin/spark,wangyum/spark,shaneknapp/spark,pronix/spark,metamx/spark,aray/spark,alunarbeach/spark,HyukjinKwon/spark,michalsenkyr/spark,eyalfa/spark,haowu80s/spark,saltstar/spark,huang1900/spark,wzhfy/spark,icexelloss/spark,dhruve/spa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