query.c

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// query.c ... query scan functions
// part of Multi-attribute Linear-hashed Files
// Manage creating and using Query objects
// Last modified by John Shepherd, July 2019

#include "defs.h"
#include "query.h"
#include "reln.h"
#include "tuple.h"

// A suggestion ... you can change however you like

struct QueryRep {
	Reln    rel;       // need to remember Relation info
	Bits    known;     // the hash value from MAH
	Bits    unknown;   // the unknown bits from MAH
	PageID  curpage;   // current page in scan
	int     is_ovflow; // are we in the overflow pages?
	Offset  curtup;    // offset of current tuple within page
	//TODO
};

// take a query string (e.g. "1234,?,abc,?")
// set up a QueryRep object for the scan

Query startQuery(Reln r, char *q)
{
	Query new = malloc(sizeof(struct QueryRep));
	assert(new != NULL);
	// TODO
	// Partial algorithm:
	// form known bits from known attributes
	// form unknown bits from '?' attributes
	// compute PageID of first page
	//   using known bits and first "unknown" value
	// set all values in QueryRep object
	return new;
}

// get next tuple during a scan

Tuple getNextTuple(Query q)
{
	// TODO
	// Partial algorithm:
	// if (more tuples in current page)
	//    get next matching tuple from current page
	// else if (current page has overflow)
	//    move to overflow page
	//    grab first matching tuple from page
	// else
	//    move to "next" bucket
	//    grab first matching tuple from data page
	// endif
	// if (current page has no matching tuples)
	//    go to next page (try again)
	// endif
	return NULL;
}

// clean up a QueryRep object and associated data

void closeQuery(Query q)
{
	// TODO
}