Index: docs/P3-UseCaseModel/UseCase0006.md
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+# Use-case 0006 — View portfolio and transaction history
+
+**Initiating actor:** Trader
+
+**Other actors:** —
+
+A Trader inspects their current holdings, unrealised P/L, cash balance and recent ledger.
+
+## Scenario
+
+### Portfolio
+
+1. Trader chooses "View portfolio".
+2. System queries the `v_portfolio` view:
+
+   ```sql
+   SELECT symbol,
+          quantity,
+          COALESCE(avg_price,      0),
+          COALESCE(current_price,  0),
+          COALESCE(market_value,   0),
+          COALESCE(unrealized_pnl, 0)
+     FROM project.v_portfolio
+    WHERE user_id = $1
+      AND quantity > 0
+    ORDER BY symbol;
+   ```
+3. System displays the rows and a computed summary:
+
+   ```sql
+   SELECT available_balance, invested_balance
+     FROM project.users
+    WHERE id = $1;
+   ```
+
+### Transaction history
+
+1. Trader chooses "View transaction history".
+2. System queries the last 20 ledger entries:
+
+   ```sql
+   SELECT created_at, type, amount, currency, COALESCE(description, '')
+     FROM project.transactions
+    WHERE user_id = $1
+    ORDER BY created_at DESC
+    LIMIT 20;
+   ```
+
+### Reference — how `v_portfolio` is defined
+
+```sql
+CREATE OR REPLACE VIEW project.v_portfolio AS
+SELECT h.user_id,
+       c.symbol,
+       h.quantity,
+       h.avg_price,
+       lp.price                                AS current_price,
+       (h.quantity * lp.price)                 AS market_value,
+       (h.quantity * (lp.price - h.avg_price)) AS unrealized_pnl
+  FROM project.holdings h
+  JOIN project.crypto   c ON c.id = h.crypto_id
+  LEFT JOIN project.markets m
+         ON m.crypto_id = c.id AND m.quote_currency = 'USD'
+  LEFT JOIN project.v_latest_prices lp
+         ON lp.market_id = m.id;
+```