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Overview
Comment:Enable constant expression factoring even if no tables are read and no transaction is started.
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SHA1: a45b87713c0afca2be2ace9500513620a024c0a2
User & Date: drh 2014-02-08 04:24:37.181
Context
2014-02-10
19:37
Experimental change to os_unix.c to delay creating a database file until it is first written. (check-in: 538f7b25e4 user: dan tags: deferred-open)
2014-02-08
13:12
Tweaks to the generated VDBE code to make it a little easier to follow. (check-in: 129217ee91 user: drh tags: trunk)
04:24
Enable constant expression factoring even if no tables are read and no transaction is started. (check-in: a45b87713c user: drh tags: trunk)
01:40
Change the OP_Trace opcode to OP_Init and give it the ability to jump to the initialization code at the bottom of the program, thus avoiding the need for an extra OP_Goto. (check-in: 192dea9731 user: drh tags: trunk)
Changes
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Changes to src/build.c.
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    /* The cookie mask contains one bit for each database file open.
    ** (Bit 0 is for main, bit 1 is for temp, and so forth.)  Bits are
    ** set for each database that is used.  Generate code to start a
    ** transaction on each used database and to verify the schema cookie
    ** on each used database.
    */
    if( db->mallocFailed==0 && pParse->cookieMask ){
    if( db->mallocFailed==0 && (pParse->cookieMask || pParse->pConstExpr) ){
      yDbMask mask;
      int iDb, i;
      assert( sqlite3VdbeGetOp(v, 0)->opcode==OP_Init );
      sqlite3VdbeJumpHere(v, 0);
      for(iDb=0, mask=1; iDb<db->nDb; mask<<=1, iDb++){
        if( (mask & pParse->cookieMask)==0 ) continue;
        sqlite3VdbeUsesBtree(v, iDb);
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  mask = ((yDbMask)1)<<iDb;
  if( (pToplevel->cookieMask & mask)==0 ){
    pToplevel->cookieMask |= mask;
    pToplevel->cookieValue[iDb] = db->aDb[iDb].pSchema->schema_cookie;
    if( !OMIT_TEMPDB && iDb==1 ){
      sqlite3OpenTempDatabase(pToplevel);
    }
    if( pToplevel==pParse && OptimizationEnabled(db,SQLITE_FactorOutConst) ){
      pParse->okConstFactor = 1;
    }
  }
}

/*
** If argument zDb is NULL, then call sqlite3CodeVerifySchema() for each 
** attached database. Otherwise, invoke it for the database named zDb only.
*/
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Changes to src/select.c.
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** If an error occurs, return NULL and leave a message in pParse.
*/
Vdbe *sqlite3GetVdbe(Parse *pParse){
  Vdbe *v = pParse->pVdbe;
  if( v==0 ){
    v = pParse->pVdbe = sqlite3VdbeCreate(pParse);
    if( v ) sqlite3VdbeAddOp0(v, OP_Init);
    if( pParse->pToplevel==0
     && OptimizationEnabled(pParse->db,SQLITE_FactorOutConst)
    ){
      pParse->okConstFactor = 1;
    }

  }
  return v;
}


/*
** Compute the iLimit and iOffset fields of the SELECT based on the
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