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-/*
-** 2015-08-18
-**
-** The author disclaims copyright to this source code. In place of
-** a legal notice, here is a blessing:
-**
-** May you do good and not evil.
-** May you find forgiveness for yourself and forgive others.
-** May you share freely, never taking more than you give.
-**
-*************************************************************************
-**
-** This file demonstrates how to create a table-valued-function using
-** a virtual table. This demo implements the generate_series() function
-** which gives similar results to the eponymous function in PostgreSQL.
-** Examples:
-**
-** SELECT * FROM generate_series(0,100,5);
-**
-** The query above returns integers from 0 through 100 counting by steps
-** of 5.
-**
-** SELECT * FROM generate_series(0,100);
-**
-** Integers from 0 through 100 with a step size of 1.
-**
-** SELECT * FROM generate_series(20) LIMIT 10;
-**
-** Integers 20 through 29.
-**
-** HOW IT WORKS
-**
-** The generate_series "function" is really a virtual table with the
-** following schema:
-**
-** CREATE TABLE generate_series(
-** value,
-** start HIDDEN,
-** stop HIDDEN,
-** step HIDDEN
-** );
-**
-** Function arguments in queries against this virtual table are translated
-** into equality constraints against successive hidden columns. In other
-** words, the following pairs of queries are equivalent to each other:
-**
-** SELECT * FROM generate_series(0,100,5);
-** SELECT * FROM generate_series WHERE start=0 AND stop=100 AND step=5;
-**
-** SELECT * FROM generate_series(0,100);
-** SELECT * FROM generate_series WHERE start=0 AND stop=100;
-**
-** SELECT * FROM generate_series(20) LIMIT 10;
-** SELECT * FROM generate_series WHERE start=20 LIMIT 10;
-**
-** The generate_series virtual table implementation leaves the xCreate method
-** set to NULL. This means that it is not possible to do a CREATE VIRTUAL
-** TABLE command with "generate_series" as the USING argument. Instead, there
-** is a single generate_series virtual table that is always available without
-** having to be created first.
-**
-** The xBestIndex method looks for equality constraints against the hidden
-** start, stop, and step columns, and if present, it uses those constraints
-** to bound the sequence of generated values. If the equality constraints
-** are missing, it uses 0 for start, 4294967295 for stop, and 1 for step.
-** xBestIndex returns a small cost when both start and stop are available,
-** and a very large cost if either start or stop are unavailable. This
-** encourages the query planner to order joins such that the bounds of the
-** series are well-defined.
-*/
-#include "wx_sqlite3ext.h"
-SQLITE_EXTENSION_INIT1
-#include <assert.h>
-#include <string.h>
-
-#ifndef SQLITE_OMIT_VIRTUALTABLE
-
-
-/* series_cursor is a subclass of wx_sqlite3_vtab_cursor which will
-** serve as the underlying representation of a cursor that scans
-** over rows of the result
-*/
-typedef struct series_cursor series_cursor;
-struct series_cursor {
- wx_sqlite3_vtab_cursor base; /* Base class - must be first */
- int isDesc; /* True to count down rather than up */
- wx_sqlite3_int64 iRowid; /* The rowid */
- wx_sqlite3_int64 iValue; /* Current value ("value") */
- wx_sqlite3_int64 mnValue; /* Mimimum value ("start") */
- wx_sqlite3_int64 mxValue; /* Maximum value ("stop") */
- wx_sqlite3_int64 iStep; /* Increment ("step") */
-};
-
-/*
-** The seriesConnect() method is invoked to create a new
-** series_vtab that describes the generate_series virtual table.
-**
-** Think of this routine as the constructor for series_vtab objects.
-**
-** All this routine needs to do is:
-**
-** (1) Allocate the series_vtab object and initialize all fields.
-**
-** (2) Tell SQLite (via the wx_sqlite3_declare_vtab() interface) what the
-** result set of queries against generate_series will look like.
-*/
-static int seriesConnect(
- wx_sqlite3 *db,
- void *pAux,
- int argc, const char *const*argv,
- wx_sqlite3_vtab **ppVtab,
- char **pzErr
-){
- wx_sqlite3_vtab *pNew;
- int rc;
-
-/* Column numbers */
-#define SERIES_COLUMN_VALUE 0
-#define SERIES_COLUMN_START 1
-#define SERIES_COLUMN_STOP 2
-#define SERIES_COLUMN_STEP 3
-
- rc = wx_sqlite3_declare_vtab(db,
- "CREATE TABLE x(value,start hidden,stop hidden,step hidden)");
- if( rc==SQLITE_OK ){
- pNew = *ppVtab = wx_sqlite3_malloc( sizeof(*pNew) );
- if( pNew==0 ) return SQLITE_NOMEM;
- memset(pNew, 0, sizeof(*pNew));
- }
- return rc;
-}
-
-/*
-** This method is the destructor for series_cursor objects.
-*/
-static int seriesDisconnect(wx_sqlite3_vtab *pVtab){
- wx_sqlite3_free(pVtab);
- return SQLITE_OK;
-}
-
-/*
-** Constructor for a new series_cursor object.
-*/
-static int seriesOpen(wx_sqlite3_vtab *p, wx_sqlite3_vtab_cursor **ppCursor){
- series_cursor *pCur;
- pCur = wx_sqlite3_malloc( sizeof(*pCur) );
- if( pCur==0 ) return SQLITE_NOMEM;
- memset(pCur, 0, sizeof(*pCur));
- *ppCursor = &pCur->base;
- return SQLITE_OK;
-}
-
-/*
-** Destructor for a series_cursor.
-*/
-static int seriesClose(wx_sqlite3_vtab_cursor *cur){
- wx_sqlite3_free(cur);
- return SQLITE_OK;
-}
-
-
-/*
-** Advance a series_cursor to its next row of output.
-*/
-static int seriesNext(wx_sqlite3_vtab_cursor *cur){
- series_cursor *pCur = (series_cursor*)cur;
- if( pCur->isDesc ){
- pCur->iValue -= pCur->iStep;
- }else{
- pCur->iValue += pCur->iStep;
- }
- pCur->iRowid++;
- return SQLITE_OK;
-}
-
-/*
-** Return values of columns for the row at which the series_cursor
-** is currently pointing.
-*/
-static int seriesColumn(
- wx_sqlite3_vtab_cursor *cur, /* The cursor */
- wx_sqlite3_context *ctx, /* First argument to wx_sqlite3_result_...() */
- int i /* Which column to return */
-){
- series_cursor *pCur = (series_cursor*)cur;
- wx_sqlite3_int64 x = 0;
- switch( i ){
- case SERIES_COLUMN_START: x = pCur->mnValue; break;
- case SERIES_COLUMN_STOP: x = pCur->mxValue; break;
- case SERIES_COLUMN_STEP: x = pCur->iStep; break;
- default: x = pCur->iValue; break;
- }
- wx_sqlite3_result_int64(ctx, x);
- return SQLITE_OK;
-}
-
-/*
-** Return the rowid for the current row. In this implementation, the
-** first row returned is assigned rowid value 1, and each subsequent
-** row a value 1 more than that of the previous.
-*/
-static int seriesRowid(wx_sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
- series_cursor *pCur = (series_cursor*)cur;
- *pRowid = pCur->iRowid;
- return SQLITE_OK;
-}
-
-/*
-** Return TRUE if the cursor has been moved off of the last
-** row of output.
-*/
-static int seriesEof(wx_sqlite3_vtab_cursor *cur){
- series_cursor *pCur = (series_cursor*)cur;
- if( pCur->isDesc ){
- return pCur->iValue < pCur->mnValue;
- }else{
- return pCur->iValue > pCur->mxValue;
- }
-}
-
-/* True to cause run-time checking of the start=, stop=, and/or step=
-** parameters. The only reason to do this is for testing the
-** constraint checking logic for virtual tables in the SQLite core.
-*/
-#ifndef SQLITE_SERIES_CONSTRAINT_VERIFY
-# define SQLITE_SERIES_CONSTRAINT_VERIFY 0
-#endif
-
-/*
-** This method is called to "rewind" the series_cursor object back
-** to the first row of output. This method is always called at least
-** once prior to any call to seriesColumn() or seriesRowid() or
-** seriesEof().
-**
-** The query plan selected by seriesBestIndex is passed in the idxNum
-** parameter. (idxStr is not used in this implementation.) idxNum
-** is a bitmask showing which constraints are available:
-**
-** 1: start=VALUE
-** 2: stop=VALUE
-** 4: step=VALUE
-**
-** Also, if bit 8 is set, that means that the series should be output
-** in descending order rather than in ascending order.
-**
-** This routine should initialize the cursor and position it so that it
-** is pointing at the first row, or pointing off the end of the table
-** (so that seriesEof() will return true) if the table is empty.
-*/
-static int seriesFilter(
- wx_sqlite3_vtab_cursor *pVtabCursor,
- int idxNum, const char *idxStr,
- int argc, wx_sqlite3_value **argv
-){
- series_cursor *pCur = (series_cursor *)pVtabCursor;
- int i = 0;
- if( idxNum & 1 ){
- pCur->mnValue = wx_sqlite3_value_int64(argv[i++]);
- }else{
- pCur->mnValue = 0;
- }
- if( idxNum & 2 ){
- pCur->mxValue = wx_sqlite3_value_int64(argv[i++]);
- }else{
- pCur->mxValue = 0xffffffff;
- }
- if( idxNum & 4 ){
- pCur->iStep = wx_sqlite3_value_int64(argv[i++]);
- if( pCur->iStep<1 ) pCur->iStep = 1;
- }else{
- pCur->iStep = 1;
- }
- for(i=0; i<argc; i++){
- if( wx_sqlite3_value_type(argv[i])==SQLITE_NULL ){
- /* If any of the constraints have a NULL value, then return no rows.
- ** See ticket https://www.sqlite.org/src/info/fac496b61722daf2 */
- pCur->mnValue = 1;
- pCur->mxValue = 0;
- break;
- }
- }
- if( idxNum & 8 ){
- pCur->isDesc = 1;
- pCur->iValue = pCur->mxValue;
- if( pCur->iStep>0 ){
- pCur->iValue -= (pCur->mxValue - pCur->mnValue)%pCur->iStep;
- }
- }else{
- pCur->isDesc = 0;
- pCur->iValue = pCur->mnValue;
- }
- pCur->iRowid = 1;
- return SQLITE_OK;
-}
-
-/*
-** SQLite will invoke this method one or more times while planning a query
-** that uses the generate_series virtual table. This routine needs to create
-** a query plan for each invocation and compute an estimated cost for that
-** plan.
-**
-** In this implementation idxNum is used to represent the
-** query plan. idxStr is unused.
-**
-** The query plan is represented by bits in idxNum:
-**
-** (1) start = $value -- constraint exists
-** (2) stop = $value -- constraint exists
-** (4) step = $value -- constraint exists
-** (8) output in descending order
-*/
-static int seriesBestIndex(
- wx_sqlite3_vtab *tab,
- wx_sqlite3_index_info *pIdxInfo
-){
- int i; /* Loop over constraints */
- int idxNum = 0; /* The query plan bitmask */
- int startIdx = -1; /* Index of the start= constraint, or -1 if none */
- int stopIdx = -1; /* Index of the stop= constraint, or -1 if none */
- int stepIdx = -1; /* Index of the step= constraint, or -1 if none */
- int nArg = 0; /* Number of arguments that seriesFilter() expects */
-
- const struct wx_sqlite3_index_constraint *pConstraint;
- pConstraint = pIdxInfo->aConstraint;
- for(i=0; i<pIdxInfo->nConstraint; i++, pConstraint++){
- if( pConstraint->usable==0 ) continue;
- if( pConstraint->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
- switch( pConstraint->iColumn ){
- case SERIES_COLUMN_START:
- startIdx = i;
- idxNum |= 1;
- break;
- case SERIES_COLUMN_STOP:
- stopIdx = i;
- idxNum |= 2;
- break;
- case SERIES_COLUMN_STEP:
- stepIdx = i;
- idxNum |= 4;
- break;
- }
- }
- if( startIdx>=0 ){
- pIdxInfo->aConstraintUsage[startIdx].argvIndex = ++nArg;
- pIdxInfo->aConstraintUsage[startIdx].omit= !SQLITE_SERIES_CONSTRAINT_VERIFY;
- }
- if( stopIdx>=0 ){
- pIdxInfo->aConstraintUsage[stopIdx].argvIndex = ++nArg;
- pIdxInfo->aConstraintUsage[stopIdx].omit = !SQLITE_SERIES_CONSTRAINT_VERIFY;
- }
- if( stepIdx>=0 ){
- pIdxInfo->aConstraintUsage[stepIdx].argvIndex = ++nArg;
- pIdxInfo->aConstraintUsage[stepIdx].omit = !SQLITE_SERIES_CONSTRAINT_VERIFY;
- }
- if( (idxNum & 3)==3 ){
- /* Both start= and stop= boundaries are available. This is the
- ** the preferred case */
- pIdxInfo->estimatedCost = (double)(2 - ((idxNum&4)!=0));
- pIdxInfo->estimatedRows = 1000;
- if( pIdxInfo->nOrderBy==1 ){
- if( pIdxInfo->aOrderBy[0].desc ) idxNum |= 8;
- pIdxInfo->orderByConsumed = 1;
- }
- }else{
- /* If either boundary is missing, we have to generate a huge span
- ** of numbers. Make this case very expensive so that the query
- ** planner will work hard to avoid it. */
- pIdxInfo->estimatedCost = (double)2147483647;
- pIdxInfo->estimatedRows = 2147483647;
- }
- pIdxInfo->idxNum = idxNum;
- return SQLITE_OK;
-}
-
-/*
-** This following structure defines all the methods for the
-** generate_series virtual table.
-*/
-static wx_sqlite3_module seriesModule = {
- 0, /* iVersion */
- 0, /* xCreate */
- seriesConnect, /* xConnect */
- seriesBestIndex, /* xBestIndex */
- seriesDisconnect, /* xDisconnect */
- 0, /* xDestroy */
- seriesOpen, /* xOpen - open a cursor */
- seriesClose, /* xClose - close a cursor */
- seriesFilter, /* xFilter - configure scan constraints */
- seriesNext, /* xNext - advance a cursor */
- seriesEof, /* xEof - check for end of scan */
- seriesColumn, /* xColumn - read data */
- seriesRowid, /* xRowid - read data */
- 0, /* xUpdate */
- 0, /* xBegin */
- 0, /* xSync */
- 0, /* xCommit */
- 0, /* xRollback */
- 0, /* xFindMethod */
- 0, /* xRename */
-};
-
-#endif /* SQLITE_OMIT_VIRTUALTABLE */
-
-#ifdef _WIN32
-__declspec(dllexport)
-#endif
-int wx_sqlite3_series_init(
- wx_sqlite3 *db,
- char **pzErrMsg,
- const wx_sqlite3_api_routines *pApi
-){
- int rc = SQLITE_OK;
- SQLITE_EXTENSION_INIT2(pApi);
-#ifndef SQLITE_OMIT_VIRTUALTABLE
- if( wx_sqlite3_libversion_number()<3008012 ){
- *pzErrMsg = wx_sqlite3_mprintf(
- "generate_series() requires SQLite 3.8.12 or later");
- return SQLITE_ERROR;
- }
- rc = wx_sqlite3_create_module(db, "generate_series", &seriesModule, 0);
-#endif
- return rc;
-}
-
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