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Overview
Comment:A new implementation for the sqlite3ExprImpliesExpr() theorem prover that does a better job of answering TRUE to "(NOT A) OR B" when B is a NOT NULL expression.
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SHA3-256: b3413197f57711f04102d8cc6ff1e8ddbe0f5f2bcb6e1989cf314fa97f0ff7f1
User & Date: drh 2019-05-11 19:36:03
Context
2019-05-13
11:52
Fix an assert() failure in fts5 that could occur when processing a corrupt database. check-in: f158c048 user: dan tags: trunk
2019-05-11
19:36
A new implementation for the sqlite3ExprImpliesExpr() theorem prover that does a better job of answering TRUE to "(NOT A) OR B" when B is a NOT NULL expression. check-in: b3413197 user: drh tags: trunk
16:14
When considering partial indexes, do not assume that a "CASE x ..." expression implies "x IS NOT NULL". check-in: 1b243032 user: dan tags: trunk
Changes
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Changes to src/expr.c.

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*/
int sqlite3ExprCompareSkip(Expr *pA, Expr *pB, int iTab){
  return sqlite3ExprCompare(0,
             sqlite3ExprSkipCollate(pA),
             sqlite3ExprSkipCollate(pB),
             iTab);
}







































































/*
** Return true if we can prove the pE2 will always be true if pE1 is
** true.  Return false if we cannot complete the proof or if pE2 might
** be false.  Examples:
**
**     pE1: x==5       pE2: x==5             Result: true
................................................................................
  if( pE2->op==TK_OR
   && (sqlite3ExprImpliesExpr(pParse, pE1, pE2->pLeft, iTab)
             || sqlite3ExprImpliesExpr(pParse, pE1, pE2->pRight, iTab) )
  ){
    return 1;
  }
  if( pE2->op==TK_NOTNULL
   && pE1->op!=TK_ISNULL
   && pE1->op!=TK_IS
   && pE1->op!=TK_ISNOT
   && pE1->op!=TK_OR
   && pE1->op!=TK_CASE
  ){
    Expr *pX = sqlite3ExprSkipCollate(pE1->pLeft);
    testcase( pX!=pE1->pLeft );
    if( sqlite3ExprCompare(pParse, pX, pE2->pLeft, iTab)==0 ) return 1;

  }
  return 0;
}

/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur







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*/
int sqlite3ExprCompareSkip(Expr *pA, Expr *pB, int iTab){
  return sqlite3ExprCompare(0,
             sqlite3ExprSkipCollate(pA),
             sqlite3ExprSkipCollate(pB),
             iTab);
}

/*
** Return non-zero if Expr p can only be true if pNN is not NULL.
*/
static int exprImpliesNotNull(
  Parse *pParse,      /* Parsing context */
  Expr *p,            /* The expression to be checked */
  Expr *pNN,          /* The expression that is NOT NULL */
  int iTab,           /* Table being evaluated */
  int seenNot         /* True if p is an operand of NOT */
){
  assert( p );
  assert( pNN );
  if( sqlite3ExprCompare(pParse, p, pNN, iTab)==0 ) return 1;
  switch( p->op ){
    case TK_IN: {
      if( seenNot && ExprHasProperty(p, EP_xIsSelect) ) return 0;
      assert( ExprHasProperty(p,EP_xIsSelect)
           || (p->x.pList!=0 && p->x.pList->nExpr>0) );
      return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
    }
    case TK_BETWEEN: {
      ExprList *pList = p->x.pList;
      assert( pList!=0 );
      assert( pList->nExpr==2 );
      if( seenNot ) return 0;
      if( exprImpliesNotNull(pParse, pList->a[0].pExpr, pNN, iTab, seenNot)
       || exprImpliesNotNull(pParse, pList->a[1].pExpr, pNN, iTab, seenNot)
      ){
        return 1;
      }
      return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
    }
    case TK_EQ:
    case TK_NE:
    case TK_LT:
    case TK_LE:
    case TK_GT:
    case TK_GE:
    case TK_PLUS:
    case TK_MINUS:
    case TK_STAR:
    case TK_REM:
    case TK_BITAND:
    case TK_BITOR:
    case TK_SLASH:
    case TK_LSHIFT:
    case TK_RSHIFT: 
    case TK_CONCAT: {
      if( exprImpliesNotNull(pParse, p->pRight, pNN, iTab, seenNot) ) return 1;
      /* Fall thru into the next case */
    }
    case TK_SPAN:
    case TK_COLLATE:
    case TK_BITNOT:
    case TK_UPLUS:
    case TK_UMINUS: {
      return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
    }
    case TK_TRUTH: {
      if( seenNot ) return 0;
      if( p->op2!=TK_IS ) return 0;
      return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, seenNot);
    }
    case TK_NOT: {
      return exprImpliesNotNull(pParse, p->pLeft, pNN, iTab, 1);
    }
  }
  return 0;
}

/*
** Return true if we can prove the pE2 will always be true if pE1 is
** true.  Return false if we cannot complete the proof or if pE2 might
** be false.  Examples:
**
**     pE1: x==5       pE2: x==5             Result: true
................................................................................
  if( pE2->op==TK_OR
   && (sqlite3ExprImpliesExpr(pParse, pE1, pE2->pLeft, iTab)
             || sqlite3ExprImpliesExpr(pParse, pE1, pE2->pRight, iTab) )
  ){
    return 1;
  }
  if( pE2->op==TK_NOTNULL
   && exprImpliesNotNull(pParse, pE1, pE2->pLeft, iTab, 0)




  ){



    return 1;
  }
  return 0;
}

/*
** This is the Expr node callback for sqlite3ExprImpliesNotNullRow().
** If the expression node requires that the table at pWalker->iCur