mysql - 如果其他字段没有值，如何显示 mysql join 语句中的所有字段

Question

下面的脚本仅显示表 Issuemail 和 amount 上的数据。我希望所有数据都应该显示在表格问题邮件中，如果金额不在金额表中，则金额将变为 o....... 卡号和条形码在发行表中是唯一的，不会重复......金额卡号可以重复，但卡号和条形码不会一起重复......

Select issuemail.borrowernumber,
  issuemail.cardnumber,
  issuemail.firstname,
  issuemail.surname,
  issuemail.title,
  issuemail.author,
  issuemail.barcode,
  issuemail.issuedate,
  issuemail.date_due,
  amount.amount
From issuemail Inner Join
  amount On amount.cardnumber = issuemail.cardnumber And amount.barcode =
    issuemail.barcode 

Answer 1

尝试使用左连接来代替......就像

    Select issuemail.borrowernumber,
    issuemail.cardnumber,
    issuemail.firstname,
    issuemail.surname,
    issuemail.title,
    issuemail.author,
    issuemail.barcode,
    issuemail.issuedate,
    issuemail.date_due,
    amount.amount
    From issuemail Left Join
    amount On amount.cardnumber = issuemail.cardnumber And amount.barcode =
    issuemail.barcode