Mysql 复杂sql查询中的左连接

嗨，伙计们，我有个问题

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

这将输出以下内容：

问题是查询不显示另一种货币代码KRW，该货币代码在tb\U cash\U交易中没有数据。以tb_货币表示的示例

如何解决这个问题？

试试这个

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