Hash join: Difference between revisions
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=={{header|REXX}}== |
=={{header|REXX}}== |
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<lang rexx>/*REXX |
<lang rexx>/*REXX program demonstrates the classic hash join algorithm for two relations.*/ |
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S. = ; R. = |
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S.1 = 27 'Jonah' ; R.1 = 'Jonah Whales' |
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S.2 = 18 'Alan' ; R.2 = 'Jonah Spiders' |
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S.3 = 28 'Glory' ; R.3 = 'Alan Ghosts' |
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S.4 = 18 'Popeye' ; R.4 = 'Alan Zombies' |
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S.5 = 28 'Alan' ; R.5 = 'Glory Buffy' |
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hash.= /*initialize the hash table. |
hash.= /*initialize the hash table (array). */ |
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do #=1 while S.#\==''; |
do #=1 while S.#\==''; parse var S.# age name /*extract information*/ |
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hash.name=hash.name # /*build a hash table entry |
hash.name=hash.name # /*build a hash table entry with its idx*/ |
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end /*#*/ /* [↑] REXX does the heavy work.*/ |
end /*#*/ /* [↑] REXX does the heavy work here. */ |
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#=#-1 /*adjust for DO loop (#) overage.*/ |
#=#-1 /*adjust for the DO loop (#) overage.*/ |
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do j=1 while R.j\=='' /*process a nemesis for a name. |
do j=1 while R.j\=='' /*process a nemesis for a name element.*/ |
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parse var R.j x nemesis /*extract name and it's nemesis. */ |
parse var R.j x nemesis /*extract the name and it's nemesis. */ |
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if hash.x=='' then do |
if hash.x=='' then do; #=#+1 /*Not in hash? Then a new name; bump #*/ |
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#= |
S.#=',' x /*add a new name to the S table. */ |
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hash.x=# /* " " " " " " hash " */ |
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end /* [↑] this DO isn't used today. */ |
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do k=1 for words(hash.x); _=word(hash.x,k) /*get the pointer.*/ |
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S._=S._ nemesis /*add the nemesis ──► applicable hash. */ |
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S._=S._ nemesis /*add nemesis──► applicable hash.*/ |
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end /*k*/ |
end /*k*/ |
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end /*j*/ |
end /*j*/ |
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_='─' /*character used for |
_='─' /*the character used for the separator.*/ |
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pad=left('',6-2) /*spacing used in |
pad=left('',6-2) /*spacing used in header and the output*/ |
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say pad center('age',3) pad center('name',20 |
say pad center('age',3) pad center('name',20 } pad center('nemesis',30 ) |
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say pad center('───',3) pad center('' ,20,_) pad center('' ,30,_) |
say pad center('───',3) pad center('' ,20,_) pad center('' ,30,_) |
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do n=1 for #; parse var S.n age name nems /*get |
do n=1 for #; parse var S.n age name nems /*get information.*/ |
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if nems=='' then iterate |
if nems=='' then iterate /*No nemesis? Skip*/ |
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say pad right(age,3) pad center(name,20) pad nems /* |
say pad right(age,3) pad center(name,20) pad nems /*display an S. */ |
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end /*n*/ |
end /*n*/ |
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/*stick a fork in it, we're done.*/</lang> |
/*stick a fork in it, we're all done. */</lang> |
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'''output''' using the in-code relations (data): |
'''output''' using the in-code relations (data): |
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<pre> |
<pre> |
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