SQLite

** for any single row of the table with cursor iCur.  In other words, the
** expression must not refer to any non-deterministic function nor any
** table other than iCur.
*/
int sqlite3ExprIsTableConstant(Expr *p, int iCur){
  return exprIsConst(p, 3, iCur);
}

/*
** Check pExpr to see if it is an invariant constraint on data source pSrc.
** This is an optimization.  False negatives will perhaps cause slower
** queries, but false positives will yield incorrect answers.  So when in
** double, return 0.
**
** To be an invariant constraint, the following must be true:
**
**   (1)  pExpr cannot refer to any table other than pSrc->iCursor.
**
**   (2)  pExpr cannot use subqueries or non-deterministic functions.
**
**   (*)  ** Not applicable to this branch **
**
**   (4)  If pSrc is the right operand of a LEFT JOIN, then...
**         (4a)  pExpr must come from an ON clause..
**         (4b)  and specifically the ON clause associated with the LEFT JOIN.
**
**   (5)  If pSrc is not the right operand of a LEFT JOIN or the left
**        operand of a RIGHT JOIN, then pExpr must be from the WHERE
**        clause, not an ON clause.
*/
int sqlite3ExprIsTableConstraint(Expr *pExpr, const SrcItem *pSrc){
  if( pSrc->fg.jointype & JT_LEFT ){
    if( !ExprHasProperty(pExpr, EP_FromJoin) ) return 0;    /* rule (4a) */
    if( pExpr->w.iRightJoinTable!=pSrc->iCursor ) return 0; /* rule (4b) */
  }else{
    if( ExprHasProperty(pExpr, EP_FromJoin) ) return 0;     /* rule (5) */
  }
  return sqlite3ExprIsTableConstant(pExpr, pSrc->iCursor);  /* rules (1), (2) */
}


/*
** sqlite3WalkExpr() callback used by sqlite3ExprIsConstantOrGroupBy().
*/
static int exprNodeIsConstantOrGroupBy(Walker *pWalker, Expr *pExpr){
  ExprList *pGroupBy = pWalker->u.pGroupBy;

** Return 0 if no changes are made and non-zero if one or more WHERE clause
** terms are duplicated into the subquery.
*/
static int pushDownWhereTerms(
  Parse *pParse,        /* Parse context (for malloc() and error reporting) */
  Select *pSubq,        /* The subquery whose WHERE clause is to be augmented */
  Expr *pWhere,         /* The WHERE clause of the outer query */
  SrcItem *pSrc         /* The subquery term of the outer FROM clause */

){
  Expr *pNew;
  int nChng = 0;
  if( pWhere==0 ) return 0;
  if( pSubq->selFlags & (SF_Recursive|SF_MultiPart) ) return 0;

#ifndef SQLITE_OMIT_WINDOWFUNC

  }
#endif

  if( pSubq->pLimit!=0 ){
    return 0; /* restriction (3) */
  }
  while( pWhere->op==TK_AND ){
    nChng += pushDownWhereTerms(pParse, pSubq, pWhere->pRight, pSrc);

    pWhere = pWhere->pLeft;
  }

#if 0  /* Legacy code. Checks now done by sqlite3ExprIsTableConstraint() */
  if( isLeftJoin
   && (ExprHasProperty(pWhere,EP_FromJoin)==0
         || pWhere->w.iRightJoinTable!=iCursor)
  ){
    return 0; /* restriction (4) */
  }
  if( ExprHasProperty(pWhere,EP_FromJoin)
   && pWhere->w.iRightJoinTable!=iCursor 
  ){
    return 0; /* restriction (5) */
  }
#endif

  if( sqlite3ExprIsTableConstraint(pWhere, pSrc) ){
    nChng++;
    pSubq->selFlags |= SF_PushDown;
    while( pSubq ){
      SubstContext x;
      pNew = sqlite3ExprDup(pParse->db, pWhere, 0);
      unsetJoinExpr(pNew, -1);
      x.pParse = pParse;
      x.iTable = pSrc->iCursor;
      x.iNewTable = pSrc->iCursor;
      x.isLeftJoin = 0;
      x.pEList = pSubq->pEList;
      pNew = substExpr(&x, pNew);
#ifndef SQLITE_OMIT_WINDOWFUNC
      if( pSubq->pWin && 0==pushDownWindowCheck(pParse, pSubq, pNew) ){
        /* Restriction 6c has prevented push-down in this case */
        sqlite3ExprDelete(pParse->db, pNew);

    /* Make copies of constant WHERE-clause terms in the outer query down
    ** inside the subquery.  This can help the subquery to run more efficiently.
    */
    if( OptimizationEnabled(db, SQLITE_PushDown)
     && (pItem->fg.isCte==0 
         || (pItem->u2.pCteUse->eM10d!=M10d_Yes && pItem->u2.pCteUse->nUse<2))
     && pushDownWhereTerms(pParse, pSub, p->pWhere, pItem)

    ){
#if SELECTTRACE_ENABLED
      if( sqlite3SelectTrace & 0x100 ){
        SELECTTRACE(0x100,pParse,p,
            ("After WHERE-clause push-down into subquery %d:\n", pSub->selId));
        sqlite3TreeViewSelect(0, p, 0);
      }

int sqlite3ExprIdToTrueFalse(Expr*);
int sqlite3ExprTruthValue(const Expr*);
int sqlite3ExprIsConstant(Expr*);
int sqlite3ExprIsConstantNotJoin(Expr*);
int sqlite3ExprIsConstantOrFunction(Expr*, u8);
int sqlite3ExprIsConstantOrGroupBy(Parse*, Expr*, ExprList*);
int sqlite3ExprIsTableConstant(Expr*,int);
int sqlite3ExprIsTableConstraint(Expr*,const SrcItem*);
#ifdef SQLITE_ENABLE_CURSOR_HINTS
int sqlite3ExprContainsSubquery(Expr*);
#endif
int sqlite3ExprIsInteger(const Expr*, int*);
int sqlite3ExprCanBeNull(const Expr*);
int sqlite3ExprNeedsNoAffinityChange(const Expr*, char);
int sqlite3IsRowid(const char*);

  idxCols = 0;
  for(pTerm=pWC->a; pTerm<pWCEnd; pTerm++){
    Expr *pExpr = pTerm->pExpr;
    /* Make the automatic index a partial index if there are terms in the
    ** WHERE clause (or the ON clause of a LEFT join) that constrain which
    ** rows of the target table (pSrc) that can be used. */
    if( (pTerm->wtFlags & TERM_VIRTUAL)==0

     && sqlite3ExprIsTableConstraint(pExpr, pSrc)
    ){
      pPartial = sqlite3ExprAnd(pParse, pPartial,
                                sqlite3ExprDup(pParse->db, pExpr, 0));
    }
    if( termCanDriveIndex(pTerm, pSrc, notReady) ){
      int iCol;
      Bitmask cMask;

    sqlite3VdbeAddOp2(v, OP_Blob, (int)sz, pLevel->regFilter);

    addrTop = sqlite3VdbeAddOp1(v, OP_Rewind, iCur); VdbeCoverage(v);
    pWCEnd = &pWInfo->sWC.a[pWInfo->sWC.nTerm];
    for(pTerm=pWInfo->sWC.a; pTerm<pWCEnd; pTerm++){
      Expr *pExpr = pTerm->pExpr;
      if( (pTerm->wtFlags & TERM_VIRTUAL)==0
       && sqlite3ExprIsTableConstraint(pExpr, pItem)
      ){
        sqlite3ExprIfFalse(pParse, pTerm->pExpr, addrCont, SQLITE_JUMPIFNULL);
      }
    }
    if( pLoop->wsFlags & WHERE_IPK ){
      int r1 = sqlite3GetTempReg(pParse);
      sqlite3VdbeAddOp2(v, OP_Rowid, iCur, r1);

  INSERT INTO t11 VALUES(NULL);
  INSERT INTO t12 VALUES('notnull');
}
do_execsql_test autoindex1-1020 {
  SELECT count(*) FROM t11 LEFT JOIN t12 WHERE t12.y IS t11.w;
} 0

# 2022-04-25
# https://sqlite.org/forum/forumpost/0d3200f4f3bcd3a3
#
reset_db
do_execsql_test autoindex-1100 {
  CREATE TABLE t1(a INT, b INT);
  CREATE TABLE t2(c INT, d INT);
  CREATE TABLE t3(e TEXT, f TEXT);
  INSERT INTO t1 VALUES(1, 1);
  INSERT INTO t2 VALUES(1, 2);
  INSERT INTO t3 VALUES('abc', 'def');
} {}
do_execsql_test autoindex-1110 {
  SELECT * FROM t1, t2 LEFT JOIN t3 ON (t2.d=1) WHERE t2.c = +t1.a;
} {1 1 1 2 {} {}}
do_execsql_test autoindex-1120 {
  SELECT * FROM t1 LEFT JOIN t2 ON (t2.c=+t1.a) LEFT JOIN t3 ON (t2.d IS NULL);
} {1 1 1 2 {} {}}

finish_test