我想查询一个问题
及其所有答案
。以下两个函数工作得很好。问题是我认为这应该在一个函数中通过一个查询来完成。 (为简洁起见,我删除了错误检查)。
func QuestionById(id string) (*Question, error) {
question := new(Question)
_ = db.QueryRow("select * from question where question.id = ?", id).Scan(
&question.Id,
&question.LessonId,
&question.Body,
&question.Type,
)
return question, nil
}
func AnswersByQuestionId(id string) ([]*Answer, error) {
rows, _ := db.Query("select * from answer where question_id = ?", id)
defer rows.Close()
answers := make([]*Answer, 0)
for rows.Next() {
answer := new(Answer)
_ = rows.Scan(&answer.Id, &answer.Body, &answer.QuestionId, &answer.Correct)
answers = append(answers, answer)
}
_ = rows.Err()
return answers, nil
}
我想以这种方式(或类似方式)使用连接查询:
func QuestionByIdAndAnswers(id string) (*Question, []*Answer error) {
rows, _ := db.Query("select * from question join answer on question.id = answer.question_id where question.id = ?", id)
// more stuff here
return question, answers, nil
}
最佳答案
一般来说应该是这样的:
func QuestionByIdAndAnswers(id string) (*Question, []*Answer, error) {
query := `
SELECT q.id, q.body, a.id, a.question_id, a.body
FROM question AS q
JOIN answer AS a ON q.id = a.question_id
WHERE q.id = ?
`
rows, err := db.Query(query, id)
checkErr(err)
question := &Question{}
for rows.Next() {
answer := &Answer{}
err = rows.Scan(
&question.ID,
&question.Body,
&answer.ID,
&answer.QuestionID,
&answer.Body,
)
checkErr(err)
question.Answers = append(question.Answers, answer)
}
return question, question.Answers, nil
}
请注意,我特意换了:
SELECT *
到 SELECT q.id, q.body, a.id, a.question_id, a.body
旨在避免以下错误:
紧急情况:sql:Scan 中预期有 6 个目标参数,而不是 5 个
在表中添加或删除某些列时可能会发生这种情况,因此此查询更健壮。
这只是基本实现,您可以使用更多字段扩展它...
PS:为简洁起见,函数 checkErr
也被省略了。
关于mysql - Golang db.Query with sql join,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45637808/