在复杂的SQL查询中左联接

Question

嗨，我有这个查询

SELECT currency_code, SUM(
CASE
WHEN TYPE = 'cash_in'
THEN amount
END ) AS cash_in, SUM(
CASE
WHEN TYPE = 'cash_out'
THEN amount
END ) AS cash_out, SUM(
CASE
WHEN TYPE = 'cash_in'
THEN amount
ELSE - amount
END ) AS balance
FROM tb_cash_transaction
LEFT JOIN tb_currency ON tb_currency.CURRENCY_ID = tb_cash_transaction.CURRENCY_ID
WHERE TYPE IN (
'cash_in', 'cash_out'
)
GROUP BY currency_code

这将输出：

问题是查询不显示tb_cash_transaction中没有数据的另一个currency_code KRW。 tb_currency中的示例

如何解决呢？

Answer 1

尝试这个

SELECT currency_code, SUM(
CASE
WHEN TYPE = 'cash_in'
THEN amount
END ) AS cash_in, SUM(
CASE
WHEN TYPE = 'cash_out'
THEN amount
END ) AS cash_out, SUM(
CASE
WHEN TYPE = 'cash_in'
THEN amount
ELSE - amount
END ) AS balance
FROM tb_currency 
LEFT JOIN tb_cash_transaction ON tb_currency.CURRENCY_ID = tb_cash_transaction.CURRENCY_ID AND tb_cash_transaction.TYPE IN (
'cash_in', 'cash_out'
)
GROUP BY currency_code