英文:
Access second row of MySQL query result in Go
问题
我正在运行一个在Go中的MySQL查询。我想要访问查询结果的第二行。我知道可以使用以下代码：
for rows.Next() {}
但是我不想为了访问第二行而运行一个循环（然后在迭代第二次后中断循环）。该怎么办？
以下是代码片段：
rows, err := db.Query("SELECT status, ts FROM events WHERE node = ? ORDER BY ts DESC LIMIT 2", testNode.ID)defer rows.Close()if err != nil {t.Error("Some Error" + err.Error())}isNext := rows.Next()if isNext == false {t.Error("No rows in query result")}rows.Scan(&status)// 如何使用第二行？
请注意，我只会返回翻译好的部分，不会回答关于翻译的问题。
英文:
I am running a MySQL query in Go. I want access the second row of the query result. I know I can use
for rows.Next {}
But I don't want to run a loop for accessing the second row (and then breaking the loop after it iterates the second time).
What to do?
Here is a code snippet:
rows,err:= db.Query("SELECT status,ts FROM events WHERE node = ? order by ts desc limit 2", testNode.ID);defer rows.Close()if ( err!= nil){t.Error("Some Error" + err.Error())}isNext:=rows.Next()if(isNext == false) {t.Error(" No rows in query result")}rows.Scan(&status)// What to do to use second row ?
答案1
得分: 1
坚持使用DB.Query()
如果你要丢弃第一行，那么从数据库中检索它就没有意义。
使用LIMIT 1, 1来丢弃第一个结果并将结果限制为1行（请查看LIMIT的文档：MySQL SELECT语法）。然后简单地继续读取第一行，它将是查询结果的第二行：
q := "SELECT status, ts FROM events WHERE node = ? order by ts desc limit 1, 1"rows, err := db.Query(query, testNode.ID)if err != nil {t.Error("Error:", err)return}defer rows.Close()if !rows.Next() {t.Error("No result")return}if err := rows.Scan(&status); err != nil {t.Error("Failed to scan:", err)return}// All good, use statusfmt.Println("Status:", status)
更多使用LIMIT的示例：
SELECT * FROM tbl LIMIT 5,10; # 检索第6-15行SELECT * FROM tbl LIMIT 5; # 检索前5行
使用DB.QueryRow()
如果你预期最多只有1行结果，你也可以使用DB.QueryRow()，结果会更加简洁：
q := "SELECT status, ts FROM events WHERE node = ? order by ts desc limit 1, 1"if err := db.QueryRow(query, testNode.ID).Scan(&status); err != nil {t.Error("Failed to scan, no result?")return}// All good, use statusfmt.Println("Status:", status)
英文:
Sticking to DB.Query()
If you're going to discard the first row, there is no point in retrieving it from the database.
Use LIMIT 1, 1 to discard the first result and limit the result to 1 row (check out the doc of LIMIT at: MySQL SELECT syntax). Then simply proceed reading the first row which will be the 2nd row of your query result:
q := "SELECT status, ts FROM events WHERE node = ? order by ts desc limit 1, 1"rows, err := db.Query(query, testNode.ID);if err != nil {t.Error("Error:", err)return}defer rows.Close()if !rows.Next() {t.Error("No result")return}if err := rows.Scan(&status); err != nil {t.Error("Failed to scan:", err)return}// All good, use statusfmt.Println("Status:", status)
More examples using LIMIT:
SELECT * FROM tbl LIMIT 5,10; # Retrieve rows 6-15SELECT * FROM tbl LIMIT 5; # Retrieve first 5 rows
Using to DB.QueryRow()
If you're expecting at most 1 row, you may also use DB.QueryRow() and the result will be much more compact:
q := "SELECT status, ts FROM events WHERE node = ? order by ts desc limit 1, 1"if err := db.QueryRow(query, testNode.ID).Scan(&status); err != nil {t.Error("Failed to scan, no result?")return}// All good, use statusfmt.Println("Status:", status)
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论