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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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