First Time a Wallet Goes Negative

SQL practice question · Hard · Window Functions · PayPal

Replay each account's wallet transactions in order of `txn_ts` (ties broken by `txn_id`). CREDIT adds `amount`, DEBIT subtracts it; transactions with status 'FAILED' are ignored. Find the FIRST successful transaction after which the running balance is below 0 (exactly 0 is not negative). Return `account_id`, `txn_id`, `txn_ts`, `balance_after` (ROUND 2) for accounts that ever went negative. Order by `account_id`.

Table: wallet_txns

Schema of wallet_txns
ColumnType
txn_idINTEGER
account_idTEXT
txn_tsTIMESTAMP
txn_typeTEXT
amountREAL
statusTEXT
Sample rows of wallet_txns
txn_idaccount_idtxn_tstxn_typeamountstatus
1A12026-10-01 09:00:00CREDIT100SUCCESS
2A12026-10-01 10:00:00DEBIT30SUCCESS
3A12026-10-02 08:00:00DEBIT80SUCCESS
4A12026-10-03 08:00:00CREDIT50SUCCESS
5A22026-10-01 09:00:00CREDIT50SUCCESS
6A22026-10-01 09:30:00DEBIT60FAILED
7A22026-10-01 10:00:00DEBIT40SUCCESS
8A32026-10-01 11:00:00DEBIT20SUCCESS
Expected output on the sample data
account_idtxn_idtxn_tsbalance_after
A132026-10-02 08:00:00-10
A382026-10-01 11:00:00-20

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