SQLite

 #undef pTrigger
#endif
#ifdef tmask
 #undef tmask
#endif

/*
** Meanings of bits in of pWalker->eCode for 
** sqlite3ExprReferencesUpdatedColumn()
*/
#define CKCNSTRNT_COLUMN   0x01    /* CHECK constraint uses a changing column */
#define CKCNSTRNT_ROWID    0x02    /* CHECK constraint references the ROWID */

/* This is the Walker callback from sqlite3ExprReferencesUpdatedColumn().
*  Set bit 0x01 of pWalker->eCode if pWalker->eCode to 0 and if this
** expression node references any of the
** columns that are being modifed by an UPDATE statement.
*/
static int checkConstraintExprNode(Walker *pWalker, Expr *pExpr){
  if( pExpr->op==TK_COLUMN ){
    assert( pExpr->iColumn>=0 || pExpr->iColumn==-1 );
    if( pExpr->iColumn>=0 ){
      if( pWalker->u.aiCol[pExpr->iColumn]>=0 ){

}

/*
** pExpr is a CHECK constraint on a row that is being UPDATE-ed.  The
** only columns that are modified by the UPDATE are those for which
** aiChng[i]>=0, and also the ROWID is modified if chngRowid is true.
**
** Return true if CHECK constraint pExpr uses any of the
** changing columns (or the rowid if it is changing).  In other words,
** return true if this CHECK constraint must be validated for
** the new row in the UPDATE statement.
**
** 2018-09-15: pExpr might also be an expression for an index-on-expressions.
** The operation of this routine is the same - return true if an only if
** the expression uses one or more of columns identified by the second and
** third arguments.
*/
int sqlite3ExprReferencesUpdatedColumn(
  Expr *pExpr,    /* The expression to be checked */
  int *aiChng,    /* aiChng[x]>=0 if column x changed by the UPDATE */
  int chngRowid   /* True if UPDATE changes the rowid */
){
  Walker w;
  memset(&w, 0, sizeof(w));
  w.eCode = 0;
  w.xExprCallback = checkConstraintExprNode;
  w.u.aiCol = aiChng;
  sqlite3WalkExpr(&w, pExpr);
  if( !chngRowid ){
    testcase( (w.eCode & CKCNSTRNT_ROWID)!=0 );
    w.eCode &= ~CKCNSTRNT_ROWID;
  }
  testcase( w.eCode==0 );
  testcase( w.eCode==CKCNSTRNT_COLUMN );
  testcase( w.eCode==CKCNSTRNT_ROWID );
  testcase( w.eCode==(CKCNSTRNT_ROWID|CKCNSTRNT_COLUMN) );
  return w.eCode!=0;
}

/*
** Generate code to do constraint checks prior to an INSERT or an UPDATE
** on table pTab.
**
** The regNewData parameter is the first register in a range that contains

  if( pTab->pCheck && (db->flags & SQLITE_IgnoreChecks)==0 ){
    ExprList *pCheck = pTab->pCheck;
    pParse->iSelfTab = -(regNewData+1);
    onError = overrideError!=OE_Default ? overrideError : OE_Abort;
    for(i=0; i<pCheck->nExpr; i++){
      int allOk;
      Expr *pExpr = pCheck->a[i].pExpr;
      if( aiChng
       && !sqlite3ExprReferencesUpdatedColumn(pExpr, aiChng, pkChng)
      ){
        /* The check constraints do not reference any of the columns being
        ** updated so there is no point it verifying the check constraint */
        continue;
      }
      allOk = sqlite3VdbeMakeLabel(v);
      sqlite3VdbeVerifyAbortable(v, onError);
      sqlite3ExprIfTrue(pParse, pExpr, allOk, SQLITE_JUMPIFNULL);
      if( onError==OE_Ignore ){
        sqlite3VdbeGoto(v, ignoreDest);
      }else{
        char *zName = pCheck->a[i].zName;

int sqlite3ExprNeedsNoAffinityChange(const Expr*, char);
int sqlite3IsRowid(const char*);
void sqlite3GenerateRowDelete(
    Parse*,Table*,Trigger*,int,int,int,i16,u8,u8,u8,int);
void sqlite3GenerateRowIndexDelete(Parse*, Table*, int, int, int*, int);
int sqlite3GenerateIndexKey(Parse*, Index*, int, int, int, int*,Index*,int);
void sqlite3ResolvePartIdxLabel(Parse*,int);
int sqlite3ExprReferencesUpdatedColumn(Expr*,int*,int);
void sqlite3GenerateConstraintChecks(Parse*,Table*,int*,int,int,int,int,
                                     u8,u8,int,int*,int*,Upsert*);
#ifdef SQLITE_ENABLE_NULL_TRIM
  void sqlite3SetMakeRecordP5(Vdbe*,Table*);
#else
# define sqlite3SetMakeRecordP5(A,B)
#endif

  }
#ifndef SQLITE_OMIT_FLOATING_POINT
  if( pTab->aCol[i].affinity==SQLITE_AFF_REAL ){
    sqlite3VdbeAddOp1(v, OP_RealAffinity, iReg);
  }
#endif
}

/*
** Check to see if column iCol of index pIdx references any of the
** columns defined by aXRef and chngRowid.  Return true if it does
** and false if not.
**
** The iCol-th column of pIdx will be an expression.
**
** aXRef[j] will be non-negative if column j of the original table is
** being updated.  chngRowid will be true if the rowid of the table is
** being updated.
*/
static int indexExprRefsUpdatedColumn(
  Index *pIdx,      /* The index containing the expression to analyze */
  int iCol,         /* Which column of the index is the expression */
  int *aXRef,       /* aXRef[j]>=0 if column j is being updated */
  int chngRowid     /* true if the rowid is being updated */
){
  assert( pIdx->aColExpr!=0 );
  assert( pIdx->aColExpr->a[iCol].pExpr!=0 );
  return sqlite3ExprReferencesUpdatedColumn(pIdx->aColExpr->a[iCol].pExpr,
                                            aXRef,chngRowid);
}

/*
** Process an UPDATE statement.
**
**   UPDATE OR IGNORE table_wxyz SET a=b, c=d WHERE e<5 AND f NOT NULL;
**          \_______/ \________/     \______/       \________________/
*            onError   pTabList      pChanges             pWhere

  pTabList->a[0].colUsed = IsVirtual(pTab) ? ALLBITS : 0;

  hasFK = sqlite3FkRequired(pParse, pTab, aXRef, chngKey);

  /* There is one entry in the aRegIdx[] array for each index on the table
  ** being updated.  Fill in aRegIdx[] with a register number that will hold
  ** the key for accessing each index.


  */
  for(j=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, j++){
    int reg;
    if( chngKey || hasFK>1 || pIdx->pPartIdxWhere || pIdx==pPk ){
      reg = ++pParse->nMem;
      pParse->nMem += pIdx->nColumn;
    }else{
      reg = 0;
      for(i=0; i<pIdx->nKeyCol; i++){
        i16 iIdxCol = pIdx->aiColumn[i];
        if( (iIdxCol>=0 && aXRef[iIdxCol]>=0)
         || iIdxCol==XN_ROWID
         || (iIdxCol==XN_EXPR
             && indexExprRefsUpdatedColumn(pIdx,i,aXRef,chngRowid))
        ){
          reg = ++pParse->nMem;
          pParse->nMem += pIdx->nColumn;
          if( (onError==OE_Replace)
           || (onError==OE_Default && pIdx->onError==OE_Replace) 
          ){
            bReplace = 1;
          }

  EXPLAIN QUERY PLAN
  SELECT * FROM t4 ORDER BY Substr(a,-2) COLLATE nocase;
} {/SCAN TABLE t4 USING INDEX i4/}
do_execsql_test 3.4.6 {
  SELECT * FROM t4 ORDER BY Substr(a,-2) COLLATE binary;
} {.ABC1 1 .ABC3 3 .abc2 2 .abc4 4}

# 2014-09-15:  Verify that UPDATEs of columns not referenced by a
# index on expression do not modify the index.
#
unset -nocomplain cnt
set cnt 0
proc refcnt {x} {
  global cnt
  incr cnt
  return $x
}
db close
sqlite3 db :memory:
db function refcnt -deterministic refcnt
do_test 4.100 {
  db eval {
    CREATE TABLE t1(a,b,c,d,e,f);
    CREATE INDEX t1abc ON t1(refcnt(a+b+c));
  }
  set ::cnt
} {0}
do_test 4.110 {
  db eval {INSERT INTO t1 VALUES(1,2,3,4,5,6);}
  set ::cnt
  # The refcnt() function is invoked once to compute the index value 
} {1}
do_test 4.120 {
  set ::cnt 0
  db eval {UPDATE t1 SET b=b+1;}
  set ::cnt
  # The refcnt() function is invoked twice, once to remove the old index
  # entry and a second time to insert the new one.
} {2}
do_test 4.130 {
  set ::cnt 0
  db eval {UPDATE t1 SET d=d+1;}
  set ::cnt
  # Refcnt() should not be invoked because that index does not change.
} {0}

finish_test