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#include <sqlite3ext.h>
#include <assert.h>
SQLITE_EXTENSION_INIT1
/*
** SQLite user defined function to use with matchinfo() to calculate the
** relevancy of an FTS match. The value returned is the relevancy score
** (a real value greater than or equal to zero). A larger value indicates
** a more relevant document.
**
** The overall relevancy returned is the sum of the relevancies of each
** column value in the FTS table. The relevancy of a column value is the
** sum of the following for each reportable phrase in the FTS query:
**
** (<hit count> / <global hit count>) * <column weight>
**
** where <hit count> is the number of instances of the phrase in the
** column value of the current row and <global hit count> is the number
** of instances of the phrase in the same column of all rows in the FTS
** table. The <column weight> is a weighting factor assigned to each
** column by the caller (see below).
**
** The first argument to this function must be the return value of the FTS
** matchinfo() function. Following this must be one argument for each column
** of the FTS table containing a numeric weight factor for the corresponding
** column. Example:
**
** CREATE VIRTUAL TABLE documents USING fts3(title, content)
**
** The following query returns the docids of documents that match the full-text
** query <query> sorted from most to least relevant. When calculating
** relevance, query term instances in the 'title' column are given twice the
** weighting of those in the 'content' column.
**
** SELECT docid FROM documents
** WHERE documents MATCH <query>
** ORDER BY rank(matchinfo(documents), 1.0, 0.5) DESC
*/
static void rankfunc(sqlite3_context *pCtx, int nVal, sqlite3_value **apVal){
unsigned int *aMatchinfo; /* Return value of matchinfo() */
int nCol; /* Number of columns in the table */
int nPhrase; /* Number of phrases in the query */
int iPhrase; /* Current phrase */
double score = 0.0; /* Value to return */
double defaultWeight = 1.0;
assert( sizeof(int)==4 );
/* Check that the number of arguments passed to this function is correct.
** If not, jump to wrong_number_args. Set aMatchinfo to point to the array
** of unsigned integer values returned by FTS function matchinfo. Set
** nPhrase to contain the number of reportable phrases in the users full-text
** query, and nCol to the number of columns in the table.
*/
aMatchinfo = (unsigned int *)sqlite3_value_blob(apVal[0]);
nPhrase = aMatchinfo[0];
nCol = aMatchinfo[1];
if ( (nVal - 1) > nCol ) goto wrong_number_args;
/* Iterate through each phrase in the users query. */
for(iPhrase=0; iPhrase<nPhrase; iPhrase++){
int iCol; /* Current column */
/* Now iterate through each column in the users query. For each column,
** increment the relevancy score by:
**
** (<hit count> / <global hit count>) * <column weight>
**
** aPhraseinfo[] points to the start of the data for phrase iPhrase. So
** the hit count and global hit counts for each column are found in
** aPhraseinfo[iCol*3] and aPhraseinfo[iCol*3+1], respectively.
*/
unsigned int *aPhraseinfo = &aMatchinfo[2 + iPhrase*nCol*3];
for(iCol=0; iCol<nCol; iCol++){
int nHitCount = aPhraseinfo[3*iCol];
int nGlobalHitCount = aPhraseinfo[3*iCol+1];
double weight = defaultWeight;
if ( (1 + iCol) < nVal ) weight = sqlite3_value_double(apVal[1 + iCol]);
if( nHitCount>0 ){
score += ((double)nHitCount / (double)nGlobalHitCount) * weight;
}
}
}
sqlite3_result_double(pCtx, score);
return;
/* Jump here if the wrong number of arguments are passed to this function */
wrong_number_args:
sqlite3_result_error(pCtx, "wrong number of arguments to function rank()", -1);
}
/* SQLite invokes this routine once when it loads the extension.
** Create new functions, collating sequences, and virtual table
** modules here. This is usually the only exported symbol in
** the shared library.
*/
int sqlite3_extension_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi) {
SQLITE_EXTENSION_INIT2(pApi)
// rank call
sqlite3_create_function(db, "rank", -1, SQLITE_ANY, 0, rankfunc, 0, 0);
return 0;
}
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