Virtual table modules with a null xCreate method act as eponymous-only modules -
they cannot be used in a CREATE VIRTUAL TABLE statement. Add the series.c extension that implements a postgres-like generate_series virtual table to demonstrate this capability. FossilOrigin-Name: c58426dbd5ea8b8440ebcc1214f79fa63d658216
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drh
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/*
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** 2015-08-18
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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**
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** This file implements a virtual table that tries to replicate the
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** behavior of the generate_series() table-valued-function in Postgres.
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**
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** Example:
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**
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** SELECT * FROM generate_series WHERE start=1 AND stop=9 AND step=2
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**
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** Results in:
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**
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** 1 3 5 7 9
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**
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*/
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#include "sqlite3ext.h"
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SQLITE_EXTENSION_INIT1
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#include <assert.h>
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#include <string.h>
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#ifndef SQLITE_OMIT_VIRTUALTABLE
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/* A series cursor object */
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typedef struct series_cursor series_cursor;
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struct series_cursor {
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sqlite3_vtab_cursor base; /* Base class - must be first */
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sqlite3_int64 iValue; /* Current value */
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sqlite3_int64 mnValue; /* Mimimum value */
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sqlite3_int64 mxValue; /* Maximum value */
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sqlite3_int64 iStep; /* How much to increment on each step */
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};
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/* Methods for the series module */
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static int seriesConnect(
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sqlite3 *db,
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void *pAux,
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int argc, const char *const*argv,
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sqlite3_vtab **ppVtab,
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char **pzErr
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){
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sqlite3_vtab *pNew;
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pNew = *ppVtab = sqlite3_malloc( sizeof(*pNew) );
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if( pNew==0 ) return SQLITE_NOMEM;
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#define SERIES_COLUMN_VALUE 0
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#define SERIES_COLUMN_START 1
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#define SERIES_COLUMN_STOP 2
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#define SERIES_COLUMN_STEP 3
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sqlite3_declare_vtab(db,
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"CREATE TABLE x(value,start hidden,stop hidden,step hidden)");
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memset(pNew, 0, sizeof(*pNew));
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return SQLITE_OK;
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}
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static int seriesDisconnect(sqlite3_vtab *pVtab){
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sqlite3_free(pVtab);
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return SQLITE_OK;
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}
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/*
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** Open a new series cursor.
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*/
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static int seriesOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
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series_cursor *pCur;
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pCur = sqlite3_malloc( sizeof(*pCur) );
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if( pCur==0 ) return SQLITE_NOMEM;
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memset(pCur, 0, sizeof(*pCur));
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*ppCursor = &pCur->base;
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return SQLITE_OK;
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}
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/*
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** Close a series cursor.
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*/
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static int seriesClose(sqlite3_vtab_cursor *cur){
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sqlite3_free(cur);
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return SQLITE_OK;
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}
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/*
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** Advance a cursor to its next row of output
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*/
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static int seriesNext(sqlite3_vtab_cursor *cur){
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series_cursor *pCur = (series_cursor*)cur;
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pCur->iValue += pCur->iStep;
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return SQLITE_OK;
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}
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/*
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** Return the value associated with a series.
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*/
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static int seriesColumn(
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sqlite3_vtab_cursor *cur,
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sqlite3_context *ctx,
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int i
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){
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series_cursor *pCur = (series_cursor*)cur;
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sqlite3_int64 x;
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switch( i ){
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case 0: x = pCur->iValue; break;
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case 1: x = pCur->mnValue; break;
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case 2: x = pCur->mxValue; break;
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case 3: x = pCur->iStep; break;
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}
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sqlite3_result_int64(ctx, x);
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return SQLITE_OK;
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}
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/*
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** The rowid.
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*/
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static int seriesRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
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series_cursor *pCur = (series_cursor*)cur;
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*pRowid = pCur->iValue;
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return SQLITE_OK;
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}
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/*
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** Return TRUE if the last row has been output.
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*/
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static int seriesEof(sqlite3_vtab_cursor *cur){
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series_cursor *pCur = (series_cursor*)cur;
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return pCur->iValue>pCur->mxValue;
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}
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/*
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** Called to "rewind" a cursor back to the beginning so that
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** it starts its output over again. Always called at least once
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** prior to any seriesColumn, seriesRowid, or seriesEof call.
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**
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** idxNum is a bitmask showing which constraints are available:
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**
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** 1: start=VALUE
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** 2: stop=VALUE
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** 4: step=VALUE
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**
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*/
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static int seriesFilter(
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sqlite3_vtab_cursor *pVtabCursor,
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int idxNum, const char *idxStr,
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int argc, sqlite3_value **argv
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){
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series_cursor *pCur = (series_cursor *)pVtabCursor;
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int i = 0;
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if( idxNum & 1 ){
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pCur->mnValue = sqlite3_value_int64(argv[i++]);
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}else{
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pCur->mnValue = 0;
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}
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pCur->iValue = pCur->mnValue;
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if( idxNum & 2 ){
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pCur->mxValue = sqlite3_value_int64(argv[i++]);
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}else{
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pCur->mxValue = 0xffffffff;
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}
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if( idxNum & 4 ){
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pCur->iStep = sqlite3_value_int64(argv[i++]);
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}else{
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pCur->iStep = 1;
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}
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return SQLITE_OK;
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}
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/*
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** Search for terms of these forms:
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**
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** (1) start = $value
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** (2) stop = $value
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** (4) step = $value
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**
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** idxNum is an ORed combination of 1, 2, 4.
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*/
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static int seriesBestIndex(
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sqlite3_vtab *tab,
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sqlite3_index_info *pIdxInfo
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){
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int i;
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int idxNum = 0;
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int startIdx = -1;
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int stopIdx = -1;
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int stepIdx = -1;
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int nArg = 0;
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const struct sqlite3_index_constraint *pConstraint;
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pConstraint = pIdxInfo->aConstraint;
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for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
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if( pConstraint->usable==0 ) continue;
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if( pConstraint->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
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switch( pConstraint->iColumn ){
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case SERIES_COLUMN_START:
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startIdx = i;
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idxNum |= 1;
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break;
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case SERIES_COLUMN_STOP:
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stopIdx = i;
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idxNum |= 2;
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break;
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case SERIES_COLUMN_STEP:
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stepIdx = i;
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idxNum |= 4;
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break;
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}
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}
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pIdxInfo->idxNum = idxNum;
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if( startIdx>=0 ){
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pIdxInfo->aConstraintUsage[startIdx].argvIndex = ++nArg;
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pIdxInfo->aConstraintUsage[startIdx].omit = 1;
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}
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if( stopIdx>=0 ){
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pIdxInfo->aConstraintUsage[stopIdx].argvIndex = ++nArg;
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pIdxInfo->aConstraintUsage[stopIdx].omit = 1;
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}
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if( stepIdx>=0 ){
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pIdxInfo->aConstraintUsage[stepIdx].argvIndex = ++nArg;
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pIdxInfo->aConstraintUsage[stepIdx].omit = 1;
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}
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if( pIdxInfo->nOrderBy==1
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&& pIdxInfo->aOrderBy[0].desc==0
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){
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pIdxInfo->orderByConsumed = 1;
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}
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if( (idxNum & 3)==3 ){
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/* Both start= and stop= boundaries are available. This is the
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** the preferred case */
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pIdxInfo->estimatedCost = (double)1;
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}else{
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/* If either boundary is missing, we have to generate a huge span
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** of numbers. Make this case very expensive so that the query
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** planner will work hard to avoid it. */
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pIdxInfo->estimatedCost = (double)2000000000;
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}
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return SQLITE_OK;
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}
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/*
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** A virtual table module that provides read-only access to a
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** Tcl global variable namespace.
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*/
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static sqlite3_module seriesModule = {
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0, /* iVersion */
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0, /* xCreate */
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seriesConnect,
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seriesBestIndex,
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seriesDisconnect,
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0, /* xDestroy */
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seriesOpen, /* xOpen - open a cursor */
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seriesClose, /* xClose - close a cursor */
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seriesFilter, /* xFilter - configure scan constraints */
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seriesNext, /* xNext - advance a cursor */
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seriesEof, /* xEof - check for end of scan */
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seriesColumn, /* xColumn - read data */
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seriesRowid, /* xRowid - read data */
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0, /* xUpdate */
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0, /* xBegin */
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0, /* xSync */
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0, /* xCommit */
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0, /* xRollback */
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0, /* xFindMethod */
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0, /* xRename */
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};
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#endif /* SQLITE_OMIT_VIRTUALTABLE */
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#ifdef _WIN32
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__declspec(dllexport)
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#endif
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int sqlite3_series_init(
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sqlite3 *db,
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char **pzErrMsg,
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const sqlite3_api_routines *pApi
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){
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int rc = SQLITE_OK;
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SQLITE_EXTENSION_INIT2(pApi);
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#ifndef SQLITE_OMIT_VIRTUALTABLE
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rc = sqlite3_create_module(db, "generate_series", &seriesModule, 0);
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#endif
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return rc;
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}
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