fixed filter in question6 step4.md

[vibhabellutagi19]

The solution for Question 6 in step4.md is wrong.

Question - Summarise all buy and sell transactions for each member_id by generating 1 row for each member with the following additional columns:

• Bitcoin buy quantity
• Bitcoin sell quantity
• Ethereum buy quantity
• Ethereum sell quantity

Given Solution -

SELECT
  member_id,
  SUM(
    CASE
      WHEN ticker = 'BTC' AND txn_type = 'BUY' THEN quantity
      ELSE 0
    END
  ) AS btc_buy_qty,
  SUM(
    CASE
      WHEN ticker = 'BTC' AND txn_type = 'SELL' THEN quantity
      ELSE 0
    END
  ) AS btc_sell_qty,
  SUM(
    CASE
      WHEN ticker = 'ETH' AND txn_type = 'BUY' THEN quantity
      ELSE 0
    END
  ) AS eth_buy_qty,
  SUM(
    CASE
      WHEN ticker = 'BTC' AND txn_type = 'SELL' THEN quantity
      ELSE 0
    END
  ) AS eth_sell_qty
FROM trading.transactions
GROUP BY member_id;

Issue - In the last case, the ticker is filtered with BTC, it should be ETH.

Correct solution -

SELECT
  member_id,
  SUM(
    CASE
      WHEN ticker = 'BTC' AND txn_type = 'BUY' THEN quantity
      ELSE 0
    END
  ) AS btc_buy_qty,
  SUM(
    CASE
      WHEN ticker = 'BTC' AND txn_type = 'SELL' THEN quantity
      ELSE 0
    END
  ) AS btc_sell_qty,
  SUM(
    CASE
      WHEN ticker = 'ETH' AND txn_type = 'BUY' THEN quantity
      ELSE 0
    END
  ) AS eth_buy_qty,
  SUM(
    CASE
      WHEN ticker = 'ETH' AND txn_type = 'SELL' THEN quantity
      ELSE 0
    END
  ) AS eth_sell_qty
FROM trading.transactions
GROUP BY member_id;