SQLite

  ExprList *pOrderBy;   /* The ORDER BY (or GROUP BY clause) */
  int nOBSat;           /* Number of ORDER BY terms satisfied by indices */
  int iECursor;         /* Cursor number for the sorter */
  int regReturn;        /* Register holding block-output return address */
  int labelBkOut;       /* Start label for the block-output subroutine */
  int addrSortIndex;    /* Address of the OP_SorterOpen or OP_OpenEphemeral */
  int labelDone;        /* Jump here when done, ex: LIMIT reached */
  int labelOBLopt;      /* Jump here when sorter is full */
  u8 sortFlags;         /* Zero or more SORTFLAG_* bits */

#ifdef SQLITE_ENABLE_SORTER_REFERENCES
  u8 nDefer;            /* Number of valid entries in aDefer[] */
  struct DeferredCsr {
    Table *pTab;        /* Table definition */
    int iCsr;           /* Cursor number for table */
    int nKey;           /* Number of PK columns for table pTab (>=1) */
  } aDefer[4];

    ** less than LIMIT+OFFSET items or (b) the new record is smaller than 
    ** the largest record currently in the sorter. If (b) is true and there
    ** are already LIMIT+OFFSET items in the sorter, delete the largest
    ** entry before inserting the new one. This way there are never more 
    ** than LIMIT+OFFSET items in the sorter.
    **
    ** If the new record does not need to be inserted into the sorter,
    ** jump to the next iteration of the loop. If the pSort->labelOBLopt
    ** value is not zero, then it is a label of where to jump.  Otherwise,
    ** just bypass the row insert logic.  See the header comment on the
    ** sqlite3WhereOrderByLimitOptLabel() function for additional info.
    */
    int iCsr = pSort->iECursor;
    sqlite3VdbeAddOp2(v, OP_IfNotZero, iLimit, sqlite3VdbeCurrentAddr(v)+4);
    VdbeCoverage(v);
    sqlite3VdbeAddOp2(v, OP_Last, iCsr, 0);
    iSkip = sqlite3VdbeAddOp4Int(v, OP_IdxLE,
                                 iCsr, 0, regBase+nOBSat, nExpr-nOBSat);

    op = OP_SorterInsert;
  }else{
    op = OP_IdxInsert;
  }
  sqlite3VdbeAddOp4Int(v, op, pSort->iECursor, regRecord,
                       regBase+nOBSat, nBase-nOBSat);
  if( iSkip ){

    sqlite3VdbeChangeP2(v, iSkip,
         pSort->labelOBLopt ? pSort->labelOBLopt : sqlite3VdbeCurrentAddr(v));
  }
}

/*
** Add code to implement the OFFSET
*/
static void codeOffset(

      p->nSelectRow = sqlite3WhereOutputRowCount(pWInfo);
    }
    if( sDistinct.isTnct && sqlite3WhereIsDistinct(pWInfo) ){
      sDistinct.eTnctType = sqlite3WhereIsDistinct(pWInfo);
    }
    if( sSort.pOrderBy ){
      sSort.nOBSat = sqlite3WhereIsOrdered(pWInfo);
      sSort.labelOBLopt = sqlite3WhereOrderByLimitOptLabel(pWInfo);
      if( sSort.nOBSat==sSort.pOrderBy->nExpr ){
        sSort.pOrderBy = 0;
      }
    }

    /* If sorting index that was created by a prior OP_OpenEphemeral 
    ** instruction ended up not being needed, then change the OP_OpenEphemeral

void sqlite3Update(Parse*, SrcList*, ExprList*,Expr*,int,ExprList*,Expr*,
                   Upsert*);
WhereInfo *sqlite3WhereBegin(Parse*,SrcList*,Expr*,ExprList*,ExprList*,u16,int);
void sqlite3WhereEnd(WhereInfo*);
LogEst sqlite3WhereOutputRowCount(WhereInfo*);
int sqlite3WhereIsDistinct(WhereInfo*);
int sqlite3WhereIsOrdered(WhereInfo*);
int sqlite3WhereOrderByLimitOptLabel(WhereInfo*);
int sqlite3WhereIsSorted(WhereInfo*);
int sqlite3WhereContinueLabel(WhereInfo*);
int sqlite3WhereBreakLabel(WhereInfo*);
int sqlite3WhereOkOnePass(WhereInfo*, int*);
#define ONEPASS_OFF      0        /* Use of ONEPASS not allowed */
#define ONEPASS_SINGLE   1        /* ONEPASS valid for a single row update */
#define ONEPASS_MULTI    2        /* ONEPASS is valid for multiple rows */

** Return FALSE if the output needs to be sorted.
*/
int sqlite3WhereIsOrdered(WhereInfo *pWInfo){
  return pWInfo->nOBSat;
}

/*
** In the ORDER BY LIMIT optimization, if the inner-most loop is known
** to emit rows in increasing order, and if the last row emitted by the
** inner-most loop did not fit within the sorter, then we can skip all
** subsequent rows for the current iteration of the inner loop (because they
** will not fit in the sorter either) and continue with the second inner
** loop - the loop immediately outside the inner-most.
**
** When a row does not fit in the sorter (because the sorter already
** holds LIMIT+OFFSET rows that are smaller), then a jump is made to the
** label returned by this function.
**
** If the ORDER BY LIMIT optimization applies, the jump destination should
** be the continuation for the second-inner-most loop.  If the ORDER BY
** LIMIT optimization does not apply, then the jump destination should
** be the continuation for the inner-most loop.
**
** It is always safe for this routine to return the continuation of the
** inner-most loop, in the sense that a correct answer will result.  
** Returning the continuation the second inner loop is an optimization
** that might make the code run a little faster, but should not change
** the final answer.
*/
int sqlite3WhereOrderByLimitOptLabel(WhereInfo *pWInfo){
  WhereLevel *pInner;
  if( !pWInfo->bOrderedInnerLoop ){
    /* The ORDER BY LIMIT optimization does not apply.  Jump to the 
    ** continuation of the inner-most loop. */
    return pWInfo->iContinue;
  }
  pInner = &pWInfo->a[pWInfo->nLevel-1];
  if( pInner->addrNxt ) return pInner->addrNxt;
  return pInner->addrBrk;
}

/*
** Return the VDBE address or label to jump to in order to continue
** immediately with the next row of a WHERE clause.
*/
int sqlite3WhereContinueLabel(WhereInfo *pWInfo){

    Bitmask notUsed;
    int rc = wherePathSatisfiesOrderBy(pWInfo, pWInfo->pResultSet, pFrom,
                 WHERE_DISTINCTBY, nLoop-1, pFrom->aLoop[nLoop-1], &notUsed);
    if( rc==pWInfo->pResultSet->nExpr ){
      pWInfo->eDistinct = WHERE_DISTINCT_ORDERED;
    }
  }
  pWInfo->bOrderedInnerLoop = 0;
  if( pWInfo->pOrderBy ){
    if( pWInfo->wctrlFlags & WHERE_DISTINCTBY ){
      if( pFrom->isOrdered==pWInfo->pOrderBy->nExpr ){
        pWInfo->eDistinct = WHERE_DISTINCT_ORDERED;
      }
    }else{
      pWInfo->nOBSat = pFrom->isOrdered;

  DROP TABLE IF EXISTS t1;
  CREATE TABLE t1(a, b);  INSERT INTO t1 VALUES(1,2);
  DROP TABLE IF EXISTS t2;
  CREATE TABLE t2(x, y);  INSERT INTO t2 VALUES(1,3);
  CREATE INDEX t1ab ON t1(a,b);
  SELECT y FROM t1, t2 WHERE a=x AND b<=y ORDER BY b DESC;
} {3}

# Ticket https://www.sqlite.org/src/info/9936b2fa443fec03 2018-09-08
# Infinite loop due to the ORDER BY LIMIT optimization.
#
do_execsql_test 700 {
  DROP TABLE IF EXISTS t1;
  DROP TABLE IF EXISTS t2;
  CREATE TABLE t1(aa VARCHAR PRIMARY KEY NOT NULL,bb,cc,x VARCHAR(400));
  INSERT INTO t1(aa,bb,cc) VALUES('maroon','meal','lecture');
  INSERT INTO t1(aa,bb,cc) VALUES('reality','meal','catsear');
  CREATE TABLE t2(aa VARCHAR PRIMARY KEY, dd INT DEFAULT 1, ee, x VARCHAR(100));
  INSERT INTO t2(aa,dd,ee) VALUES('maroon',0,'travel'),('reality',0,'hour');
  CREATE INDEX t2x1 ON t2(dd,ee);
  ANALYZE;
  DROP TABLE IF EXISTS sqlite_stat4;
  DELETE FROM sqlite_stat1;
  INSERT INTO sqlite_stat1 VALUES
    ('t2','t2x1','3 3 3'),
    ('t2','sqlite_autoindex_t2_1','3 1'),
    ('t1','sqlite_autoindex_t1_1','2 1');
  ANALYZE sqlite_master;
  SELECT *
    FROM t1 LEFT JOIN t2 ON t1.aa=t2.aa
   WHERE t1.bb='meal'
   ORDER BY t2.dd DESC
   LIMIT 1;
} {maroon meal lecture {} maroon 0 travel {}}
do_execsql_test 710 {
  DROP TABLE t1;
  DROP TABLE t2;
  CREATE TABLE t1(aa, bb);
  INSERT INTO t1 VALUES('maroon','meal');
  CREATE TABLE t2(cc, dd, ee, x VARCHAR(100));
  INSERT INTO t2(cc,dd,ee) VALUES('maroon',1,'one');
  INSERT INTO t2(cc,dd,ee) VALUES('maroon',2,'two');
  INSERT INTO t2(cc,dd,ee) VALUES('maroon',0,'zero');
  CREATE INDEX t2ddee ON t2(dd,ee);
  CREATE INDEX t2cc ON t2(cc);
   ANALYZE;
  SELECT t2.cc, t2.dd, t2.ee FROM t1 CROSS JOIN t2 ON t1.aa=t2.cc
  ORDER BY t2.dd LIMIT 1;
} {maroon 0 zero}
do_execsql_test 720 {
  SELECT t2.cc, t2.dd, t2.ee FROM t1 CROSS JOIN t2 ON t1.aa=t2.cc
  WHERE t1.bb='meal'
  ORDER BY t2.dd LIMIT 1;
} {maroon 0 zero}

finish_test