** Code an OP_Once instruction and allocate space for its flag. Return the 
** address of the new instruction.
*/
int sqlite3CodeOnce(Parse *pParse){
  Vdbe *v = sqlite3GetVdbe(pParse);      /* Virtual machine being coded */
  return sqlite3VdbeAddOp1(v, OP_Once, pParse->nOnce++);
}

















/*
** This function is used by the implementation of the IN (...) operator.
** The pX parameter is the expression on the RHS of the IN operator, which
** might be either a list of expressions or a subquery.
**
** The job of this routine is to find or create a b-tree object that can
................................................................................
** contains a NULL.  If prRhsHasNull is not a NULL pointer and 
** if there is any chance that the (...) might contain a NULL value at
** runtime, then a register is allocated and the register number written
** to *prRhsHasNull. If there is no chance that the (...) contains a
** NULL value, then *prRhsHasNull is left unchanged.
**
** If a register is allocated and its location stored in *prRhsHasNull, then
** the value in that register will be:
**
**          0      if the (...) contains no NULL values
**          1      if the (...) does not contain NULL values
**       NULL      if we do not yet know if (...) contains NULLs
**
** If the (...) does not remain constant for the duration of the query
** (i.e. the SELECT within the (...) is a correlated subquery) then the
** value of the allocated register is reset to NULL each time the subquery
** is rerun. This allows the caller to use vdbe code equivalent to the
** following:
**
**   if( r[*prRhsHasNull] IS NULL ){
**     r[*prRhsHasNull] = <test if data structure contains null>
**   }
**
** in order to avoid running the <test if data structure contains null>
** test more often than is necessary.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prRhsHasNull){
  Select *p;                            /* SELECT to the right of IN operator */
  int eType = 0;                        /* Type of RHS table. IN_INDEX_* */
  int iTab = pParse->nTab++;            /* Cursor of the RHS table */
  int mustBeUnique;                     /* True if RHS must be unique */
................................................................................
          sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
          VdbeComment((v, "%s", pIdx->zName));
          assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
          eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];

          if( prRhsHasNull && !pTab->aCol[iCol].notNull ){
            *prRhsHasNull = ++pParse->nMem;
            sqlite3VdbeAddOp2(v, OP_Null, 0, *prRhsHasNull);
          }
          sqlite3VdbeJumpHere(v, iAddr);
        }
      }
    }
  }

................................................................................
** For a SELECT or EXISTS operator, return the register that holds the
** result.  For IN operators or if an error occurs, the return value is 0.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3CodeSubselect(
  Parse *pParse,          /* Parsing context */
  Expr *pExpr,            /* The IN, SELECT, or EXISTS operator */
  int rMayHaveNull,       /* Register that records whether NULLs exist in RHS */
  int isRowid             /* If true, LHS of IN operator is a rowid */
){
  int testAddr = -1;                      /* One-time test address */
  int rReg = 0;                           /* Register storing resulting */
  Vdbe *v = sqlite3GetVdbe(pParse);
  if( NEVER(v==0) ) return 0;
  sqlite3ExprCachePush(pParse);

  /* This code must be run in its entirety every time it is encountered
  ** if any of the following is true:
................................................................................
  **    *  The right-hand side is an expression list containing variables
  **    *  We are inside a trigger
  **
  ** If all of the above are false, then we can run this code just once
  ** save the results, and reuse the same result on subsequent invocations.
  */
  if( !ExprHasProperty(pExpr, EP_VarSelect) ){
    testAddr = sqlite3CodeOnce(pParse); VdbeCoverage(v);
  }

#ifndef SQLITE_OMIT_EXPLAIN
  if( pParse->explain==2 ){
    char *zMsg = sqlite3MPrintf(
        pParse->db, "EXECUTE %s%s SUBQUERY %d", testAddr>=0?"":"CORRELATED ",
        pExpr->op==TK_IN?"LIST":"SCALAR", pParse->iNextSelectId
    );
    sqlite3VdbeAddOp4(v, OP_Explain, pParse->iSelectId, 0, 0, zMsg, P4_DYNAMIC);
  }
#endif

  switch( pExpr->op ){
    case TK_IN: {
      char affinity;              /* Affinity of the LHS of the IN */
      int addr;                   /* Address of OP_OpenEphemeral instruction */
      Expr *pLeft = pExpr->pLeft; /* the LHS of the IN operator */
      KeyInfo *pKeyInfo = 0;      /* Key information */

      if( rMayHaveNull ){
        sqlite3VdbeAddOp2(v, OP_Null, 0, rMayHaveNull);
      }

      affinity = sqlite3ExprAffinity(pLeft);

      /* Whether this is an 'x IN(SELECT...)' or an 'x IN(<exprlist>)'
      ** expression it is handled the same way.  An ephemeral table is 
      ** filled with single-field index keys representing the results
      ** from the SELECT or the <exprlist>.
      **
................................................................................
          int iValToIns;

          /* If the expression is not constant then we will need to
          ** disable the test that was generated above that makes sure
          ** this code only executes once.  Because for a non-constant
          ** expression we need to rerun this code each time.
          */
          if( testAddr>=0 && !sqlite3ExprIsConstant(pE2) ){
            sqlite3VdbeChangeToNoop(v, testAddr);
            testAddr = -1;
          }

          /* Evaluate the expression and insert it into the temp table */
          if( isRowid && sqlite3ExprIsInteger(pE2, &iValToIns) ){
            sqlite3VdbeAddOp3(v, OP_InsertInt, pExpr->iTable, r2, iValToIns);
          }else{
            r3 = sqlite3ExprCodeTarget(pParse, pE2, r1);
................................................................................
      }
      rReg = dest.iSDParm;
      ExprSetVVAProperty(pExpr, EP_NoReduce);
      break;
    }
  }

  if( testAddr>=0 ){




    sqlite3VdbeJumpHere(v, testAddr);
  }
  sqlite3ExprCachePop(pParse);

  return rReg;
}
#endif /* SQLITE_OMIT_SUBQUERY */

................................................................................
**
** The left-hand side (LHS) is a scalar expression.  The right-hand side (RHS)
** is an array of zero or more values.  The expression is true if the LHS is
** contained within the RHS.  The value of the expression is unknown (NULL)
** if the LHS is NULL or if the LHS is not contained within the RHS and the
** RHS contains one or more NULL values.
**
** This routine generates code will jump to destIfFalse if the LHS is not 
** contained within the RHS.  If due to NULLs we cannot determine if the LHS
** is contained in the RHS then jump to destIfNull.  If the LHS is contained
** within the RHS then fall through.
*/
static void sqlite3ExprCodeIN(
  Parse *pParse,        /* Parsing and code generating context */
  Expr *pExpr,          /* The IN expression */
................................................................................
      sqlite3VdbeAddOp4Int(v, OP_NotFound, pExpr->iTable, destIfFalse, r1, 1);
      VdbeCoverage(v);
    }else{
      /* In this branch, the RHS of the IN might contain a NULL and
      ** the presence of a NULL on the RHS makes a difference in the
      ** outcome.
      */
      int j1, j2;

      /* First check to see if the LHS is contained in the RHS.  If so,
      ** then the presence of NULLs in the RHS does not matter, so jump
      ** over all of the code that follows.


      */
      j1 = sqlite3VdbeAddOp4Int(v, OP_Found, pExpr->iTable, 0, r1, 1);
      VdbeCoverage(v);

      /* Here we begin generating code that runs if the LHS is not
      ** contained within the RHS.  Generate additional code that
      ** tests the RHS for NULLs.  If the RHS contains a NULL then
      ** jump to destIfNull.  If there are no NULLs in the RHS then
      ** jump to destIfFalse.
      */
      sqlite3VdbeAddOp2(v, OP_If, rRhsHasNull, destIfNull); VdbeCoverage(v);
      sqlite3VdbeAddOp2(v, OP_IfNot, rRhsHasNull, destIfFalse); VdbeCoverage(v);
      j2 = sqlite3VdbeAddOp4Int(v, OP_Found, pExpr->iTable, 0, rRhsHasNull, 1);
      VdbeCoverage(v);
      sqlite3VdbeAddOp2(v, OP_Integer, 0, rRhsHasNull);
      sqlite3VdbeAddOp2(v, OP_Goto, 0, destIfFalse);
      sqlite3VdbeJumpHere(v, j2);
      sqlite3VdbeAddOp2(v, OP_Integer, 1, rRhsHasNull);
      sqlite3VdbeAddOp2(v, OP_Goto, 0, destIfNull);

      /* The OP_Found at the top of this branch jumps here when true, 
      ** causing the overall IN expression evaluation to fall through.
      */
      sqlite3VdbeJumpHere(v, j1);
    }
  }
  sqlite3ReleaseTempReg(pParse, r1);
  sqlite3ExprCachePop(pParse);
  VdbeComment((v, "end IN expr"));
}

** Code an OP_Once instruction and allocate space for its flag. Return the 
** address of the new instruction.
*/
int sqlite3CodeOnce(Parse *pParse){
  Vdbe *v = sqlite3GetVdbe(pParse);      /* Virtual machine being coded */
  return sqlite3VdbeAddOp1(v, OP_Once, pParse->nOnce++);
}

/*
** Generate code that checks the single-column index table iCur to see if
** contains any NULL entries.  Cause the register at regHasNull to be set
** to a non-NULL value if iCur contains no NULLs.  Cause register regHasNull
** to be set to NULL if iCur contains one or more NULL values.
*/
static void sqlite3SetHasNullFlag(Vdbe *v, int iCur, int regHasNull){
  int j1;
  sqlite3VdbeAddOp2(v, OP_Integer, 0, regHasNull);
  j1 = sqlite3VdbeAddOp1(v, OP_Rewind, iCur); VdbeCoverage(v);
  sqlite3VdbeAddOp3(v, OP_Column, iCur, 0, regHasNull);
  sqlite3VdbeChangeP5(v, OPFLAG_TYPEOFARG);
  VdbeComment((v, "<maybe-NULL?>"));
  sqlite3VdbeJumpHere(v, j1);
}

/*
** This function is used by the implementation of the IN (...) operator.
** The pX parameter is the expression on the RHS of the IN operator, which
** might be either a list of expressions or a subquery.
**
** The job of this routine is to find or create a b-tree object that can
................................................................................
** contains a NULL.  If prRhsHasNull is not a NULL pointer and 
** if there is any chance that the (...) might contain a NULL value at
** runtime, then a register is allocated and the register number written
** to *prRhsHasNull. If there is no chance that the (...) contains a
** NULL value, then *prRhsHasNull is left unchanged.
**
** If a register is allocated and its location stored in *prRhsHasNull, then
** the value in that register will be NULL if the b-tree contains one or more
** NULL values, and it will be some non-NULL value if the b-tree contains no
** NULL values.















*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prRhsHasNull){
  Select *p;                            /* SELECT to the right of IN operator */
  int eType = 0;                        /* Type of RHS table. IN_INDEX_* */
  int iTab = pParse->nTab++;            /* Cursor of the RHS table */
  int mustBeUnique;                     /* True if RHS must be unique */
................................................................................
          sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
          VdbeComment((v, "%s", pIdx->zName));
          assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
          eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];

          if( prRhsHasNull && !pTab->aCol[iCol].notNull ){
            *prRhsHasNull = ++pParse->nMem;
            sqlite3SetHasNullFlag(v, iTab, *prRhsHasNull);
          }
          sqlite3VdbeJumpHere(v, iAddr);
        }
      }
    }
  }

................................................................................
** For a SELECT or EXISTS operator, return the register that holds the
** result.  For IN operators or if an error occurs, the return value is 0.
*/
#ifndef SQLITE_OMIT_SUBQUERY
int sqlite3CodeSubselect(
  Parse *pParse,          /* Parsing context */
  Expr *pExpr,            /* The IN, SELECT, or EXISTS operator */
  int rHasNullFlag,       /* Register that records whether NULLs exist in RHS */
  int isRowid             /* If true, LHS of IN operator is a rowid */
){
  int jmpIfDynamic = -1;                      /* One-time test address */
  int rReg = 0;                           /* Register storing resulting */
  Vdbe *v = sqlite3GetVdbe(pParse);
  if( NEVER(v==0) ) return 0;
  sqlite3ExprCachePush(pParse);

  /* This code must be run in its entirety every time it is encountered
  ** if any of the following is true:
................................................................................
  **    *  The right-hand side is an expression list containing variables
  **    *  We are inside a trigger
  **
  ** If all of the above are false, then we can run this code just once
  ** save the results, and reuse the same result on subsequent invocations.
  */
  if( !ExprHasProperty(pExpr, EP_VarSelect) ){
    jmpIfDynamic = sqlite3CodeOnce(pParse); VdbeCoverage(v);
  }

#ifndef SQLITE_OMIT_EXPLAIN
  if( pParse->explain==2 ){
    char *zMsg = sqlite3MPrintf(
        pParse->db, "EXECUTE %s%s SUBQUERY %d", jmpIfDynamic>=0?"":"CORRELATED ",
        pExpr->op==TK_IN?"LIST":"SCALAR", pParse->iNextSelectId
    );
    sqlite3VdbeAddOp4(v, OP_Explain, pParse->iSelectId, 0, 0, zMsg, P4_DYNAMIC);
  }
#endif

  switch( pExpr->op ){
    case TK_IN: {
      char affinity;              /* Affinity of the LHS of the IN */
      int addr;                   /* Address of OP_OpenEphemeral instruction */
      Expr *pLeft = pExpr->pLeft; /* the LHS of the IN operator */
      KeyInfo *pKeyInfo = 0;      /* Key information */





      affinity = sqlite3ExprAffinity(pLeft);

      /* Whether this is an 'x IN(SELECT...)' or an 'x IN(<exprlist>)'
      ** expression it is handled the same way.  An ephemeral table is 
      ** filled with single-field index keys representing the results
      ** from the SELECT or the <exprlist>.
      **
................................................................................
          int iValToIns;

          /* If the expression is not constant then we will need to
          ** disable the test that was generated above that makes sure
          ** this code only executes once.  Because for a non-constant
          ** expression we need to rerun this code each time.
          */
          if( jmpIfDynamic>=0 && !sqlite3ExprIsConstant(pE2) ){
            sqlite3VdbeChangeToNoop(v, jmpIfDynamic);
            jmpIfDynamic = -1;
          }

          /* Evaluate the expression and insert it into the temp table */
          if( isRowid && sqlite3ExprIsInteger(pE2, &iValToIns) ){
            sqlite3VdbeAddOp3(v, OP_InsertInt, pExpr->iTable, r2, iValToIns);
          }else{
            r3 = sqlite3ExprCodeTarget(pParse, pE2, r1);
................................................................................
      }
      rReg = dest.iSDParm;
      ExprSetVVAProperty(pExpr, EP_NoReduce);
      break;
    }
  }

  if( rHasNullFlag ){
    sqlite3SetHasNullFlag(v, pExpr->iTable, rHasNullFlag);
  }

  if( jmpIfDynamic>=0 ){
    sqlite3VdbeJumpHere(v, jmpIfDynamic);
  }
  sqlite3ExprCachePop(pParse);

  return rReg;
}
#endif /* SQLITE_OMIT_SUBQUERY */

................................................................................
**
** The left-hand side (LHS) is a scalar expression.  The right-hand side (RHS)
** is an array of zero or more values.  The expression is true if the LHS is
** contained within the RHS.  The value of the expression is unknown (NULL)
** if the LHS is NULL or if the LHS is not contained within the RHS and the
** RHS contains one or more NULL values.
**
** This routine generates code that jumps to destIfFalse if the LHS is not 
** contained within the RHS.  If due to NULLs we cannot determine if the LHS
** is contained in the RHS then jump to destIfNull.  If the LHS is contained
** within the RHS then fall through.
*/
static void sqlite3ExprCodeIN(
  Parse *pParse,        /* Parsing and code generating context */
  Expr *pExpr,          /* The IN expression */
................................................................................
      sqlite3VdbeAddOp4Int(v, OP_NotFound, pExpr->iTable, destIfFalse, r1, 1);
      VdbeCoverage(v);
    }else{
      /* In this branch, the RHS of the IN might contain a NULL and
      ** the presence of a NULL on the RHS makes a difference in the
      ** outcome.
      */
      int j1;

      /* First check to see if the LHS is contained in the RHS.  If so,
      ** then the answer is TRUE the presence of NULLs in the RHS does
      ** not matter.  If the LHS is not contained in the RHS, then the
      ** answer is NULL if the RHS contains NULLs and the answer is
      ** FALSE if the RHS is NULL-free.
      */
      j1 = sqlite3VdbeAddOp4Int(v, OP_Found, pExpr->iTable, 0, r1, 1);
      VdbeCoverage(v);







      sqlite3VdbeAddOp2(v, OP_IsNull, rRhsHasNull, destIfNull);


      VdbeCoverage(v);

      sqlite3VdbeAddOp2(v, OP_Goto, 0, destIfFalse);







      sqlite3VdbeJumpHere(v, j1);
    }
  }
  sqlite3ReleaseTempReg(pParse, r1);
  sqlite3ExprCachePop(pParse);
  VdbeComment((v, "end IN expr"));
}