SQLite

  Db *aDb;                      /* All backends */
  int nDb;                      /* Number of backends currently in use */
  int flags;                    /* Miscellaneous flags. See below */
  i64 lastRowid;                /* ROWID of most recent insert (see above) */
  unsigned int openFlags;       /* Flags passed to sqlite3_vfs.xOpen() */
  int errCode;                  /* Most recent error code (SQLITE_*) */
  int errMask;                  /* & result codes with this before returning */
  u16 dbOptFlags;               /* Flags to enable/disable optimizations */
  u8 autoCommit;                /* The auto-commit flag. */
  u8 temp_store;                /* 1: file 2: memory 0: default */
  u8 mallocFailed;              /* True if we have seen a malloc failure */
  u8 dfltLockMode;              /* Default locking-mode for attached dbs */
  signed char nextAutovac;      /* Autovac setting after VACUUM if >=0 */
  u8 suppressErr;               /* Do not issue error messages if true */
  u8 vtabOnConflict;            /* Value to return for s3_vtab_on_conflict() */

#define SQLITE_QueryFlattener 0x0001   /* Query flattening */
#define SQLITE_ColumnCache    0x0002   /* Column cache */
#define SQLITE_GroupByOrder   0x0004   /* GROUPBY cover of ORDERBY */
#define SQLITE_FactorOutConst 0x0008   /* Constant factoring */
#define SQLITE_IdxRealAsInt   0x0010   /* Store REAL as INT in indices */
#define SQLITE_DistinctOpt    0x0020   /* DISTINCT using indexes */
#define SQLITE_CoverIdxScan   0x0040   /* Covering index scans */
#define SQLITE_OrderByIdx     0x0180   /* ORDER BY using indices */
#define SQLITE_OrderByIdxJoin 0x0100   /* ORDER BY of joins via index */
#define SQLITE_AllOpts        0x01ff   /* All optimizations */

/*
** Macros for testing whether or not optimizations are enabled or disabled.
*/
#ifndef SQLITE_OMIT_BUILTIN_TEST
#define OptimizationDisabled(db, mask)  (((db)->dbOptFlags&(mask))!=0)
#define OptimizationEnabled(db, mask)   (((db)->dbOptFlags&(mask))==0)

    { "query-flattener",  SQLITE_QueryFlattener },
    { "column-cache",     SQLITE_ColumnCache    },
    { "groupby-order",    SQLITE_GroupByOrder   },
    { "factor-constants", SQLITE_FactorOutConst },
    { "real-as-int",      SQLITE_IdxRealAsInt   },
    { "distinct-opt",     SQLITE_DistinctOpt    },
    { "cover-idx-scan",   SQLITE_CoverIdxScan   },
    { "order-by-idx",     SQLITE_OrderByIdx     },
    { "order-by-idx-join",SQLITE_OrderByIdxJoin },
  };

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB OPT BOOLEAN");
    return TCL_ERROR;
  }

  ExprList *pOrderBy;           /* The ORDER BY clause */
  Parse *pParse = p->pParse;    /* Parser context */
  sqlite3 *db = pParse->db;     /* Database connection */
  int nPriorSat;                /* ORDER BY terms satisfied by outer loops */
  int seenRowid = 0;            /* True if an ORDER BY rowid term is seen */
  int nEqOneRow;                /* Idx columns that ref unique values */

  if( OptimizationDisabled(db, SQLITE_OrderByIdx) ) return 0;
  if( p->i==0 ){
    nPriorSat = 0;
    nEqOneRow = nEqCol;
  }else{
    if( OptimizationDisabled(db, SQLITE_OrderByIdxJoin) ) return 0;
    nPriorSat = p->aLevel[p->i-1].plan.nOBSat;
    sortOrder = bOuterRev;

          bInEst = 1;
        }else if( ALWAYS(pExpr->x.pList && pExpr->x.pList->nExpr) ){
          /* "x IN (value, value, ...)" */
          nInMul *= pExpr->x.pList->nExpr;
        }
      }else if( pTerm->eOperator & WO_ISNULL ){
        wsFlags |= WHERE_COLUMN_NULL;

      }else if( bSort && nEq==nOrdered && isOrderedTerm(p, pTerm, &bRev) ){
        nOrdered++;
      }
#ifdef SQLITE_ENABLE_STAT3
      if( nEq==0 && pProbe->aSample ) pFirstTerm = pTerm;
#endif
      used |= pTerm->prereqRight;

      testcase( bRev==2 );
      nOBSat = isSortingIndex(p, pProbe, iCur, nOrdered,
                              wsFlags, bRev&1, &bRev);
      if( nOrderBy==nOBSat ){
        bSort = 0;
        wsFlags |= WHERE_ROWID_RANGE|WHERE_COLUMN_RANGE|WHERE_ORDERBY;
      }
      if( bRev ) wsFlags |= WHERE_REVERSE;
    }

    /* If there is a DISTINCT qualifier and this index will scan rows in
    ** order of the DISTINCT expressions, clear bDist and set the appropriate
    ** flags in wsFlags. */
    if( bDist
     && isDistinctIndex(pParse, pWC, pProbe, iCur, p->pDistinct, nEq)

      DROP INDEX collate4i1;
      CREATE INDEX collate4i1 ON collate4t1(a);
    }
    count {
      SELECT a FROM collate4t1 WHERE a IN (SELECT * FROM collate4t2)
       ORDER BY rowid
    }
  } {a A 5}
  do_test collate4-2.1.8 {
    count {
      SELECT a FROM collate4t1 WHERE a IN ('z', 'a');
    }
  } {a A 5}
  do_test collate4-2.1.9 {
    execsql {

      SELECT * FROM t1 WHERE rowid+0 IN (1,2,3,1234) order by 1;
    }
  } {1 0 4 2 1 9 3 1 16 102}
  do_test where-5.3 {
    count {
      SELECT * FROM t1 WHERE w IN (-1,1,2,3) order by 1;
    }
  } {1 0 4 2 1 9 3 1 16 13}
  do_test where-5.4 {
    count {
      SELECT * FROM t1 WHERE w+0 IN (-1,1,2,3) order by 1;
    }
  } {1 0 4 2 1 9 3 1 16 102}
  do_test where-5.5 {
    count {