Hash join: Difference between revisions

<lang rexx>/*REXX program demonstrates the classic hash join algorithm for two 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 information*/

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 its nemesis. */

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

S.#=',' x /*add a new name to the S table. */

hash.x=# /* " " " " " " hash " */

end /* [↑] this DO isn't used today. */

do k=1 for words(hash.x); _=word(hash.x, k) /*getobtain the pointer.*/

S._=S._ nemesis /*add the nemesis ──► applicable hash. */

end /*k*/

end /*j*/

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

pad=left('',6-2 4) /*spacing used in 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 /*getobtain information.*/

if nems=='' then iterate /*No nemesis? Skip. */

say pad right(age,3) pad center(name,20) pad center(nems ,30) /*display an "S". */

27 Jonah Whales Spiders

18 Alan Ghosts Zombies

28 Glory Buffy

28 Alan Ghosts Zombies