SQLite

**     CREATE INDEX
**     DROP INDEX
**     creating ID lists
**     BEGIN TRANSACTION
**     COMMIT
**     ROLLBACK
**
** $Id: build.c,v 1.337 2005/07/27 20:41:44 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

/*
** This routine is called when a new SQL statement is beginning to
** be parsed.  Initialize the pParse structure as needed.

  sqliteFree(zName);
  return;
}

/*
** Fill the Index.aiRowEst[] array with default information - information
** to be used when we have no ANALYZE command to run.
**
** aiRowEst[0] is suppose to contain the number of elements in the index.
** Since we do not know, guess 1 million.  aiRowEst[1] is an estimate of the
** number of rows in the table that match any particular value of the
** first column of the index.  aiRowEst[2] is an estimate of the number
** of rows that match any particular combiniation of the first 2 columns
** of the index.  And so forth.  It must always be the case that
*
**           aiRowEst[N]<=aiRowEst[N-1]
**           aiRowEst[N]>=1
**
** Apart from that, we have little to go on besides intuition as to
** how aiRowEst[] should be initialized.  The numbers generated here
** are based on typical values found in actual indices.
*/
void sqlite3DefaultRowEst(Index *pIdx){
  int *a = pIdx->aiRowEst;
  int i;
  assert( a!=0 );
  a[0] = 1000000;
  switch( pIdx->nColumn ){
    case 1: {
      a[1] = 20;
      break;
    }
    case 2: {
      a[1] = 350;
      a[2] = 20;
      break;
    }
    default: {
      a[1] = 1250;
      a[2] = 350;
      a[3] = 20;
      for(i=pIdx->nColumn; i>=4; i--){
        a[i] = 10;
      }
    }
  }
  if( pIdx->onError!=OE_None ){


    a[pIdx->nColumn] = 1;
  }
}

/*
** This routine will drop an existing named index.  This routine
** implements the DROP INDEX statement.
*/

** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is reponsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.153 2005/07/27 20:41:44 drh Exp $
*/
#include "sqliteInt.h"

/*
** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
*/
#define BMS  (sizeof(Bitmask)*8)

  int nTerm;                   /* Number of ORDER BY terms */
  struct ExprList_item *pTerm; /* A term of the ORDER BY clause */
  sqlite3 *db = pParse->db;

  assert( pOrderBy!=0 );
  nTerm = pOrderBy->nExpr;
  assert( nTerm>0 );

  /* A UNIQUE index that is fully specified is always a sorting
  ** index.
  */
  if( pIdx->onError!=OE_None && nEqCol==pIdx->nColumn ){
    *pbRev = 0;
    return 1;
  }

  /* Match terms of the ORDER BY clause against columns of
  ** the index.
  */
  for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<pIdx->nColumn; i++){
    Expr *pExpr;       /* The expression of the ORDER BY pTerm */
    CollSeq *pColl;    /* The collating sequence of pExpr */

  p = pOrderBy->a[0].pExpr;
  if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1 ){
    *pbRev = pOrderBy->a[0].sortOrder;
    return 1;
  }
  return 0;
}

/*
** Prepare a crude estimate of the logorithm of the input value.
** The results need not be exact.  This is only used for estimating
** the total cost of performing operatings with O(logN) or O(NlogN)
** complexity.  Because N is just a guess, it is no great tragedy if
** logN is a little off.
**
** We can assume N>=1.0;
*/
static double estLog(double N){
  double logN = 1.0;
  double x = 10.0;
  while( N>x ){
    logN = logN+1.0;
    x *= 10;
  }
  return logN;
}

/*
** Find the best index for accessing a particular table.  Return a pointer
** to the index, flags that describe how the index should be used, the
** number of equality constraints and the "cost" for this index.
**
** The lowest cost index wins.  The cost is an estimate of the amount of

  /* Check for a rowid=EXPR or rowid IN (...) constraints
  */
  pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
  if( pTerm ){
    *ppIndex = 0;
    bestFlags = WHERE_ROWID_EQ;
    if( pTerm->operator & WO_EQ ){
      /* Rowid== is always the best pick.  Look no further.  Because only
      ** a single row is generated, output is always in sorted order */
      *pFlags = WHERE_ROWID_EQ;
      *pnEq = 1;
      if( pOrderBy ) *pFlags |= WHERE_ORDERBY;
      TRACE(("... best is rowid\n"));
      return 0.0;
    }else if( pTerm->operator & WO_LIST ){
      /* Rowid IN (LIST): cost is NlogN where N is the number of list
      ** elements.  */
      lowestCost = pTerm->pExpr->pList->nExpr;
      lowestCost *= estLog(lowestCost);
    }else{
      /* Rowid IN (SELECT): cost is NlogN where N is the number of rows
      ** in the result of the inner select.  We have no way to estimate
      ** that value so make a wild guess. */
      lowestCost = 200.0;
    }
    TRACE(("... rowid IN cost: %g\n", lowestCost));
  }

  /* Estimate the cost of a table scan.  If we do not know how many
  ** entries are in the table, use 1 million as a guess.
  */
  pProbe = pSrc->pTab->pIndex;
  cost = pProbe ? pProbe->aiRowEst[0] : 1000000.0;
  TRACE(("... table scan base cost: %g\n", cost));
  flags = WHERE_ROWID_RANGE;

  /* Check for constraints on a range of rowids in a table scan.
  */
  pTerm = findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE|WO_GT|WO_GE, 0);
  if( pTerm ){

    if( findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE, 0) ){
      flags |= WHERE_TOP_LIMIT;
      cost *= 0.333;  /* Guess that rowid<EXPR eliminates two-thirds or rows */
    }
    if( findTerm(pWC, iCur, -1, notReady, WO_GT|WO_GE, 0) ){
      flags |= WHERE_BTM_LIMIT;
      cost *= 0.333;  /* Guess that rowid>EXPR eliminates two-thirds of rows */
    }
    TRACE(("... rowid range reduces cost to %g\n", cost));
  }else{
    flags = 0;
  }

  /* If the table scan does not satisfy the ORDER BY clause, increase
  ** the cost by NlogN to cover the expense of sorting. */
  if( pOrderBy ){
    if( sortableByRowid(iCur, pOrderBy, &rev) ){
      flags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;

      if( rev ){
        flags |= WHERE_REVERSE;
      }
    }else{
      cost += cost*estLog(cost);
      TRACE(("... sorting increases cost to %g\n", cost));
    }
  }
  if( cost<lowestCost ){
    lowestCost = cost;
    bestFlags = flags;
  }

  /* Look at each index.
  */
  for(; pProbe; pProbe=pProbe->pNext){
    int i;                       /* Loop counter */
    double inMultiplier = 1.0;

    TRACE(("... index %s:\n", pProbe->zName));

    /* Count the number of columns in the index that are satisfied
    ** by x=EXPR constraints or x IN (...) constraints.
    */
    flags = 0;

        if( pTerm->operator & WO_SELECT ){
          inMultiplier *= 100.0;
        }else if( pTerm->operator & WO_LIST ){
          inMultiplier *= pTerm->pExpr->pList->nExpr + 1.0;
        }
      }
    }
    cost = pProbe->aiRowEst[i] * inMultiplier * estLog(inMultiplier);
    nEq = i;
    TRACE(("...... nEq=%d inMult=%g cost=%g\n", nEq, inMultiplier, cost));

    /* Look for range constraints
    */
    if( nEq<pProbe->nColumn ){
      int j = pProbe->aiColumn[nEq];
      pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);
      if( pTerm ){
        flags = WHERE_COLUMN_RANGE;
        if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){
          flags |= WHERE_TOP_LIMIT;
          cost *= 0.333;
        }
        if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){
          flags |= WHERE_BTM_LIMIT;
          cost *= 0.333;
        }
        TRACE(("...... range reduces cost to %g\n", cost));
      }
    }


    /* Add the additional cost of sorting if that is a factor.
    */
    if( pOrderBy ){
      if( (flags & WHERE_COLUMN_IN)==0 &&
        isSortingIndex(pParse, pProbe, pSrc->pTab, iCur, pOrderBy, nEq, &rev) ){
        if( flags==0 ){
          flags = WHERE_COLUMN_RANGE;
        }
        flags |= WHERE_ORDERBY;

        if( rev ){
          flags |= WHERE_REVERSE;
        }
      }else{
        cost += cost*estLog(cost);
        TRACE(("...... orderby reduces cost to %g\n", cost));
      }
    }

    /* Check to see if we can get away with using just the index without
    ** ever reading the table.  If that is the case, then halve the
    ** cost of this index.
    */
    if( flags && pSrc->colUsed < (((Bitmask)1)<<(BMS-1)) ){