MySQL 错误 : #1242 - Subquery returns more than 1 row

Question

SELECT BookId, Duedate, (SELECT Title FROM Book_Information WHERE BookId = BookId)
FROM Transaction_Information WHERE DueDate <= CURDATE() AND ReturnedDate IS NULL

book id是transaction_information中的外键。我想将图书信息表中的Title字段添加到交易信息表中

Answer 1

由于Transaction_Information.BookId 是外键，它引用Book_Information 表中的相应行，因此一个简单的INNER JOIN 会完成这项工作。

这是查询:

SELECT
TF.BookId,
TF.Duedate,
BF.Title
FROM Transaction_Information TF
INNER JOIN Book_Information BF
ON TF.BookId = BF.BookId
WHERE TF.DueDate <= CURDATE() AND TF.ReturnedDate IS NULL;