chernishev / toydbms-old Goto Github PK

The following code makes no sense:

    std::ptrdiff_t lpos1 = std::find(ln[i].begin(), ln[i].end(), ((LJoinNode*)prototype)->offset1) - ln[i].begin();
    std::ptrdiff_t lpos2 = std::find(ln[i].begin(), ln[i].end(), ((LJoinNode*)prototype)->offset2) - ln[i].begin();

    if (lpos1 <= ln.size() || lpos1 <= ln.size()) {
      if (lpos1 < lpos2)
        lpos = lpos1;
      else
        lpos = lpos2;
      break;
    }

For instance, the condition in the first if compares index in ln[i] with size of ln, which is meaningless. Also, lpos is assigned an index from ln[i] and it's later used as a column id, which makes no sense as well.

Example where this does not work: just make id column in table the last column and run demo

Assuming that fieldOrders vector should contain invariant about order of rows corresponding to that field, LJoinNode initiates it incorrectly: it assumes that all non-joined columns remain sorted in the same way as they were. However, it's clearly not the case, e.g. if we join these two tables on column A:

| A | B |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |

| A | C |
| 3 | 1 |
| 1 | 2 |
| 3 | 3 |

After join, column C will become unsorted.