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Comment:When a scalar subquery has a pre-existing "LIMIT X" then change it to "LIMIT X<>0" rather than just "LIMIT 1" so that if X is 0 the limit will still be zero. Ticket [99cd4807dc03f178]. Test cases in TH3.
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SHA3-256: 82e5dcf5c1d500ed82f398b38fdae0f30033804e897fbab3c10f1e15e2abedef
User & Date: drh 2019-09-23 11:55:22.905
Original Comment: When a scalar subquery has a pre-existing "LIMIT X" then change it to "LIMIT X<>0" rather than just "LIMIT 1" so that if X is 0 the limit will still be zero. Ticket [99cd4807dc03f178]
Context
2019-09-23
12:38
Omit the sqlite3IntTokens array constant for a code simplification. (check-in: f907395ef5 user: drh tags: trunk)
11:55
When a scalar subquery has a pre-existing "LIMIT X" then change it to "LIMIT X<>0" rather than just "LIMIT 1" so that if X is 0 the limit will still be zero. Ticket [99cd4807dc03f178]. Test cases in TH3. (check-in: 82e5dcf5c1 user: drh tags: trunk)
2019-09-21
18:49
Fix a harmless unused variable warning in the test logic. (check-in: d7673a445f user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/expr.c.
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    sqlite3VdbeAddOp3(v, OP_Null, 0, dest.iSDParm, dest.iSDParm+nReg-1);
    VdbeComment((v, "Init subquery result"));
  }else{
    dest.eDest = SRT_Exists;
    sqlite3VdbeAddOp2(v, OP_Integer, 0, dest.iSDParm);
    VdbeComment((v, "Init EXISTS result"));
  }
  pLimit = sqlite3ExprAlloc(pParse->db, TK_INTEGER,&sqlite3IntTokens[1], 0);
  if( pSel->pLimit ){









    sqlite3ExprDelete(pParse->db, pSel->pLimit->pLeft);
    pSel->pLimit->pLeft = pLimit;
  }else{


    pSel->pLimit = sqlite3PExpr(pParse, TK_LIMIT, pLimit, 0);
  }
  pSel->iLimit = 0;
  if( sqlite3Select(pParse, pSel, &dest) ){
    return 0;
  }
  pExpr->iTable = rReg = dest.iSDParm;








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    sqlite3VdbeAddOp3(v, OP_Null, 0, dest.iSDParm, dest.iSDParm+nReg-1);
    VdbeComment((v, "Init subquery result"));
  }else{
    dest.eDest = SRT_Exists;
    sqlite3VdbeAddOp2(v, OP_Integer, 0, dest.iSDParm);
    VdbeComment((v, "Init EXISTS result"));
  }

  if( pSel->pLimit ){
    /* The subquery already has a limit.  If the pre-existing limit is X
    ** then make the new limit X<>0 so that the new limit is either 1 or 0 */
    sqlite3 *db = pParse->db;
    pLimit = sqlite3ExprAlloc(db, TK_INTEGER, &sqlite3IntTokens[0], 0);
    if( pLimit ){
      pLimit->affExpr = SQLITE_AFF_NUMERIC;
      pLimit = sqlite3PExpr(pParse, TK_NE,
                            sqlite3ExprDup(db, pSel->pLimit->pLeft, 0), pLimit);
    }
    sqlite3ExprDelete(db, pSel->pLimit->pLeft);
    pSel->pLimit->pLeft = pLimit;
  }else{
    /* If there is no pre-existing limit add a limit of 1 */
    pLimit = sqlite3ExprAlloc(pParse->db, TK_INTEGER, &sqlite3IntTokens[1], 0);
    pSel->pLimit = sqlite3PExpr(pParse, TK_LIMIT, pLimit, 0);
  }
  pSel->iLimit = 0;
  if( sqlite3Select(pParse, pSel, &dest) ){
    return 0;
  }
  pExpr->iTable = rReg = dest.iSDParm;
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