SQLite

      testcase( pSelect->selFlags & SF_Distinct );
      testcase( pKeyInfo==0 ); /* Caused by OOM in sqlite3KeyInfoAlloc() */
      pCopy = sqlite3SelectDup(pParse->db, pSelect, 0);
      rc = pParse->db->mallocFailed ? 1 :sqlite3Select(pParse, pCopy, &dest);
      sqlite3SelectDelete(pParse->db, pCopy);
      sqlite3DbFree(pParse->db, dest.zAffSdst);
      if( addrBloom ){
        /* Remember that location of the Bloom filter in the P3 operand
        ** of the OP_Once that began this subroutine. tag-202407032019 */
        sqlite3VdbeGetOp(v, addrOnce)->p3 = dest.iSDParm2;
        if( dest.iSDParm2==0 ){
          /* If the Bloom filter won't actually be used, keep it small */

          sqlite3VdbeGetOp(v, addrBloom)->p1 = 10;
        }
      }
      if( rc ){
        sqlite3KeyInfoUnref(pKeyInfo);
        return;
      }
      assert( pKeyInfo!=0 ); /* OOM will cause exit after sqlite3Select() */

  }else{
    sqlite3VdbeAddOp4(v, OP_Affinity, rLhs, nVector, 0, zAff, nVector);
    if( destIfFalse==destIfNull ){
      /* Combine Step 3 and Step 5 into a single opcode */
      if( ExprHasProperty(pExpr, EP_Subrtn) ){
        const VdbeOp *pOp = sqlite3VdbeGetOp(v, pExpr->y.sub.iAddr);
        assert( pOp->opcode==OP_Once || pParse->nErr );
        if( pOp->opcode==OP_Once && pOp->p3>0 ){  /* tag-202407032019 */
          assert( OptimizationEnabled(pParse->db, SQLITE_BloomFilter) );
          sqlite3VdbeAddOp4Int(v, OP_Filter, pOp->p3, destIfFalse,
                               rLhs, nVector); VdbeCoverage(v);
        }
      }
      sqlite3VdbeAddOp4Int(v, OP_NotFound, iTab, destIfFalse,
                           rLhs, nVector); VdbeCoverage(v);

  if( (pIn1->flags & MEM_Null)==0 ){
    pOut->flags = MEM_Int;
    pOut->u.i = ~sqlite3VdbeIntValue(pIn1);
  }
  break;
}

/* Opcode: Once P1 P2 P3 * *
**
** Fall through to the next instruction the first time this opcode is
** encountered on each invocation of the byte-code program.  Jump to P2
** on the second and all subsequent encounters during the same invocation.
**
** Top-level programs determine first invocation by comparing the P1
** operand against the P1 operand on the OP_Init opcode at the beginning
** of the program.  If the P1 values differ, then fall through and make
** the P1 of this opcode equal to the P1 of OP_Init.  If P1 values are
** the same then take the jump.
**
** For subprograms, there is a bitmask in the VdbeFrame that determines
** whether or not the jump should be taken.  The bitmask is necessary
** because the self-altering code trick does not work for recursive
** triggers.
**
** The P3 operand is not used directly by this opcode.  However P3 is
** used by the code generator as follows:  If this opcode is the start
** of a subroutine and that subroutine uses a Bloom filter, then P3 will
** be the register that holds that Bloom filter.  See tag-202407032019
** in the source code for implementation details.
*/
case OP_Once: {             /* jump */
  u32 iAddr;                /* Address of this instruction */
  assert( p->aOp[0].opcode==OP_Init );
  if( p->pFrame ){
    iAddr = (int)(pOp - p->aOp);
    if( (p->pFrame->aOnce[iAddr/8] & (1<<(iAddr & 7)))!=0 ){

      WHERE (ref_1.c1) = (2)
      ORDER BY c_0 desc
    ) as subq_2
    UNION ALL
    SELECT 0 as c_0
  );
} {0}

# 2025-04-30 https://sqlite.org/forum/forumpost/792a09cb3df9e69f
# A continuation of the above.
#
do_execsql_test 6.1 {
  DROP TABLE IF EXISTS t1;
  CREATE TABLE t1(a);
  SELECT 111 IN (
    SELECT 222 FROM (SELECT 333 ORDER BY 1)
    UNION ALL
    SELECT 444 FROM (SELECT 555 FROM t1 ORDER BY 1)
  );
} 0

finish_test