Card: idx is the transaction's position in its block

The idx column was described as the trade's position within its slot, numbered separately for landed and failed rows. It is the transaction's 0-based position in its block (checked against the chain), shared by every table; (slot, idx) is the join key to signatures.

README.md

@@ -89,7 +89,7 @@ Rows are ordered by `(ts, slot, idx, failed)` within and across shards (shard `0
 | `block_time` | timestamp, UTC | block time, as a timestamp |
 | `ts` | int64 | block time, unix seconds |
 | `slot` | int64 | Solana slot |
-| `idx` | int32 | the trade's position within its slot, as the archive orders it (landed and failed rows each have their own `idx`) |
+| `idx` | int32 | the transaction's 0-based position in its block, the same number in every table of the archive: several trades in one transaction share it, and a landed and a failed row never do. With `slot` it is the transaction's key; the full archive's signatures table joins on (`slot`, `idx`) |
 | `venue` | string | `curve` (the pump.fun bonding curve) or `pumpswap` (a PumpSwap pool) |
 | `venue_code` | string | the archive's raw venue code. Curve codes are `c`, `curve`, `bonding_curve` or `0`, and any other code is PumpSwap. The coverage table lists the codes present |
 | `failed` | bool | `false`: the trade landed. `true`: the transaction tried a curve or PumpSwap trade, made it into a block and failed (`error` says why). Failed rows have no amounts and no reserves, only who tried what, the fee they paid and the error |