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Comment:Modify internal function whereLoopAdjustCost() so that it does not prefer a skip-scan over a regular index scan even if the regular scan uses a subset of the WHERE terms used by the skip-scan.
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SHA1: 88a5758dcce891eb7be15432ebdc9f80071d413b
User & Date: dan 2014-04-28 09:35:31
Context
2014-04-28
10:00
Update test script analyze3.test to account for the fact that SQLite now prefers a full-table scan over a non-covering index scan that visits a large percentage of the table rows. check-in: 35f46a55 user: dan tags: experimental-costs
09:35
Modify internal function whereLoopAdjustCost() so that it does not prefer a skip-scan over a regular index scan even if the regular scan uses a subset of the WHERE terms used by the skip-scan. check-in: 88a5758d user: dan tags: experimental-costs
08:49
Fix an error in estimating of the number of rows visited by a range scan. check-in: d491de62 user: dan tags: experimental-costs
Changes
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Changes to src/where.c.

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**
** To say "WhereLoop X is a proper subset of Y" means that X uses fewer
** WHERE clause terms than Y and that every WHERE clause term used by X is
** also used by Y.
*/
static void whereLoopAdjustCost(const WhereLoop *p, WhereLoop *pTemplate){
  if( (pTemplate->wsFlags & WHERE_INDEXED)==0 ) return;

  for(; p; p=p->pNextLoop){
    if( p->iTab!=pTemplate->iTab ) continue;
    if( (p->wsFlags & WHERE_INDEXED)==0 ) continue;

    if( whereLoopCheaperProperSubset(p, pTemplate) ){
      /* Adjust pTemplate cost downward so that it is cheaper than its 
      ** subset p */
      pTemplate->rRun = p->rRun;
      pTemplate->nOut = p->nOut - 1;
    }else if( whereLoopCheaperProperSubset(pTemplate, p) ){
      /* Adjust pTemplate cost upward so that it is costlier than p since







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**
** To say "WhereLoop X is a proper subset of Y" means that X uses fewer
** WHERE clause terms than Y and that every WHERE clause term used by X is
** also used by Y.
*/
static void whereLoopAdjustCost(const WhereLoop *p, WhereLoop *pTemplate){
  if( (pTemplate->wsFlags & WHERE_INDEXED)==0 ) return;
  if( (pTemplate->wsFlags & WHERE_SKIPSCAN)!=0 ) return;
  for(; p; p=p->pNextLoop){
    if( p->iTab!=pTemplate->iTab ) continue;
    if( (p->wsFlags & WHERE_INDEXED)==0 ) continue;
    if( (p->wsFlags & WHERE_SKIPSCAN)!=0 ) continue;
    if( whereLoopCheaperProperSubset(p, pTemplate) ){
      /* Adjust pTemplate cost downward so that it is cheaper than its 
      ** subset p */
      pTemplate->rRun = p->rRun;
      pTemplate->nOut = p->nOut - 1;
    }else if( whereLoopCheaperProperSubset(pTemplate, p) ){
      /* Adjust pTemplate cost upward so that it is costlier than p since