SQLite

    topOfLoop = sqlite3VdbeCurrentAddr(v);
    sqlite3VdbeAddOp2(v, OP_AddImm, iMem, 1);  /* Increment row counter */

    for(i=0; i<nCol; i++){
      CollSeq *pColl;
      sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, i, regCol);
      if( i==0 ){
#ifdef SQLITE_ENABLE_STAT2
        /* Check if the record that cursor iIdxCur points to contains a
        ** value that should be stored in the sqlite_stat2 table. If so,
        ** store it.  */
        int ne = sqlite3VdbeAddOp3(v, OP_Ne, iMem, 0, regNext);
        VdbeComment((v, "jump if not a sample"));
        sqlite3VdbeAddOp2(v, OP_Gosub, regGosub, addrStoreStat2);
        sqlite3VdbeAddOp2(v, OP_Copy, regCol, regSample);
        sqlite3VdbeAddOp2(v, OP_AddImm, regReady, 1);

        /* Calculate new values for regNextSample.  Where N is the number
        ** of rows in the table and S is the number of samples to take:
        **
        **   nextSample = (sampleNumber*N*2 + N)/(2*S)
        */
        sqlite3VdbeAddOp2(v, OP_AddImm, regSampleIdx, 1);
        sqlite3VdbeAddOp3(v, OP_Multiply, regSampleIdx, regCount2, regNext);
        sqlite3VdbeAddOp3(v, OP_Add, regNext, regCount, regNext);
        sqlite3VdbeAddOp3(v, OP_Divide, regSample2, regNext, regNext);
        sqlite3VdbeJumpHere(v, ne);
#endif

        /* Always record the very first row */
        addrIfNot = sqlite3VdbeAddOp1(v, OP_IfNot, iMem+1);
      }
      assert( pIdx->azColl!=0 );
      assert( pIdx->azColl[i]!=0 );
      pColl = sqlite3LocateCollSeq(pParse, pIdx->azColl[i]);
      aChngAddr[i] = sqlite3VdbeAddOp4(v, OP_Ne, regCol, 0, iMem+nCol+i+1,

#endif        
      }
      sqlite3VdbeAddOp2(v, OP_AddImm, iMem+i+1, 1);
      sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, i, iMem+nCol+i+1);
    }
    sqlite3DbFree(db, aChngAddr);

    /* End of the analysis loop. */
    /* Always jump here after updating the iMem+1...iMem+1+nCol counters */
    sqlite3VdbeResolveLabel(v, endOfLoop);

#ifdef SQLITE_ENABLE_STAT2
    /* Check if the record that cursor iIdxCur points to contains a
    ** value that should be stored in the sqlite_stat2 table. If so,
    ** store it. 
    */
    int ne = sqlite3VdbeAddOp3(v, OP_Le, regNext, 0, iMem);
    VdbeComment((v, "jump if not a sample"));
    shortJump = sqlite3VdbeAddOp1(v, OP_If, regReady);
    sqlite3VdbeAddOp2(v, OP_Copy, iMem+nCol+1, regSample);
    sqlite3VdbeJumpHere(v, shortJump);
    sqlite3VdbeAddOp2(v, OP_AddImm, regReady, 1);

    /* Calculate new values for regNextSample.  Where N is the number
    ** of rows in the table and S is the number of samples to take:
    **
    **   nextSample = (sampleNumber*N*2 + N)/(2*S)
    */
    sqlite3VdbeAddOp2(v, OP_AddImm, regSampleIdx, 1);
    sqlite3VdbeAddOp3(v, OP_Multiply, regSampleIdx, regCount2, regNext);
    sqlite3VdbeAddOp3(v, OP_Add, regNext, regCount, regNext);
    sqlite3VdbeAddOp3(v, OP_Divide, regSample2, regNext, regNext);
    sqlite3VdbeJumpHere(v, ne);
#endif

    sqlite3VdbeAddOp2(v, OP_Next, iIdxCur, topOfLoop);
    sqlite3VdbeAddOp1(v, OP_Close, iIdxCur);
#ifdef SQLITE_ENABLE_STAT2
    sqlite3VdbeAddOp2(v, OP_Gosub, regGosub, addrStoreStat2);
#endif        

    /* Store the results in sqlite_stat1.

  memAboutToChange(p, pOut);

  /* Loop through the elements that will make up the record to figure
  ** out how much space is required for the new record.
  */
  for(pRec=pData0; pRec<=pLast; pRec++){
    assert( memIsValid(pRec) );
    REGISTER_TRACE((pRec-pData0)+pOp->p1, pRec);
    if( zAffinity ){
      applyAffinity(pRec, zAffinity[pRec-pData0], encoding);
    }
    if( pRec->flags&MEM_Zero && pRec->n>0 ){
      sqlite3VdbeMemExpandBlob(pRec);
    }
    serial_type = sqlite3VdbeSerialType(pRec, file_format);

# 2011 August 5
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
# This file implements tests for the ANALYZE command under STAT2.
# Testing the logic that computes the number of copies of each sample.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# There is nothing to test if ANALYZE is disable for this build.
#
ifcapable {!analyze||!vtab||!stat2} {
  finish_test
  return
}

# Generate some test data
#
do_test analyze8-1.0 {
  set x 100
  set y 1
  set ycnt 0
  set yinc 10
  execsql {
    CREATE TABLE t1(x,y);
    ANALYZE;
    BEGIN;
    CREATE INDEX t1x ON t1(x);
    CREATE INDEX t1y ON t1(y);
  }
  for {set i 0} {$i<20} {incr i} {
    for {set j 0} {$j<300} {incr j} {
      execsql {INSERT INTO t1 VALUES($x,$y)}
      incr ycnt
      if {$ycnt>=$yinc} {set ycnt 0; incr y}
    }
    for {set j 0} {$j<100} {incr j} {
      incr x
      execsql {INSERT INTO t1 VALUES($x,$y)}
      incr ycnt
      if {$ycnt>=$yinc} {set ycnt 0; incr y}
    }
  }
  execsql {
    COMMIT;
    ANALYZE;
    SELECT sample, cnt FROM sqlite_stat2 WHERE idx='t1x' ORDER BY sampleno;
  }
} {200 301 400 301 600 301 800 301 1000 301 1200 301 1400 301 1600 301 1800 301 2000 301}
do_test analyze8-1.1 {
  execsql {
    SELECT count(*) FROM t1 WHERE x=200;
  }
} {301}

do_test analyze8-2.0 {
  execsql {
    BEGIN;
    DELETE FROM t1;
  }
  for {set x 1} {$x<200} {incr x} {
    execsql {INSERT INTO t1 VALUES($x,$x)}
  }
  for {set i 0} {$i<200} {incr i} {
    execsql {INSERT INTO t1 VALUES(999,999)}
  }
  execsql {
    COMMIT;
    ANALYZE;
    SELECT sample, cnt FROM sqlite_stat2 WHERE idx='t1x' ORDER BY sampleno;
  }
} {20 1 60 1 100 1 140 1 180 1 999 200 999 200 999 200 999 200 999 200}
do_test analyze8-2.1 {
  for {set i 0} {$i<200} {incr i} {
    execsql {INSERT INTO t1 VALUES(0,999)}
  }
  execsql {
    ANALYZE;
    SELECT sample, cnt FROM sqlite_stat2 WHERE idx='t1x' ORDER BY sampleno;
  }
} {0 200 0 200 0 200 10 1 70 1 130 1 190 1 999 200 999 200 999 200}