Hash join: Difference between revisions

<lang rexx>/*REXX pgmprogram demonstrates the classic hash join algorithm for 2two relations.*/

S. = ; ; R. =

S.1 = 27 'Jonah' ; ; R.1 = 'Jonah Whales'

S.2 = 18 'Alan' ; ; R.2 = 'Jonah Spiders'

S.3 = 28 'Glory' ; ; R.3 = 'Alan Ghosts'

S.4 = 18 'Popeye' ; ; R.4 = 'Alan Zombies'

S.5 = 28 'Alan' ; ; R.5 = 'Glory Buffy'

hash.= /*initialize the hash table (array). */

do #=1 while S.#\==''; parse var S.# age name /*extract infoinformation*/

hash.name=hash.name # /*build a hash table entry. with its idx*/

end /*#*/ /* [↑] REXX does the heavy work here. */

#=#-1 /*adjust for the DO loop (#) overage.*/

do j=1 while R.j\=='' /*process a nemesis for a name element. */

parse var R.j x nemesis /*extract the name and it's nemesis. */

if hash.x=='' then do; #=#+1 /*Not in hash? Then a new name.; bump #*/

S.#=#+1',' x /*add a new /*bumpname to the number of S entries table. */

Shash.#x=','# x /*add new" name to" the S" " " " hash " table. */

hash.x=#end /*add new[↑] name tothis theDO hashisn't tableused today. */

do k=1 for words(hash.x); end _=word(hash.x,k) /*get [↑] this DO isn't usedthe todaypointer.*/

do kS._=1S._ nemesis for words(hash.x); _=word(hash.x,k) /*getadd pointerthe nemesis ──► applicable hash. */

_='─' /*the character used for separater. the separator.*/

pad=left('',6-2) /*spacing used in hdr/sep/header and the output.*/

say pad center('age',3) pad center('name',20) } pad center('nemesis',30 )

say pad center('───',3) pad center('' ,20,_) pad center('' ,30,_)

do n=1 for #; parse var S.n age name nems /*get infoinformation. */

if nems=='' then iterate /*if no nemesis, then don't show. /*No nemesis? Skip*/

say pad right(age,3) pad center(name,20) pad nems /*showdisplay an S. */

/*stick a fork in it, we're all done. */</lang>