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

Question

下面的脚本仅显示他们在表问题邮件和金额上拥有的数据。我希望所有数据都应该显示在表问题邮件中，如果金额表中没有的话，金额将变为o.......卡号和条形码在问题表中是唯一的，不会重复...... ....金额卡号可能会重复，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

尝试使用左连接代替..喜欢

    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