Multiple rows.Next() in the same time golang sql/database - mysql

Question

I am working on a function which gets users. My problem is that I have to return the result of two queries as one result in the rows.Next() and rows1.Next() like user_id, subject, phone.
Here is what I have but it doesn't work. Could you please help me out with some suggestions:
func GetUsers() (users []Users, err error) {
users = make([]Users, 0)
rows, err := db1.Query("SELECT user_id, subject,phone FROM users limit 11")
rows1, err := db1.Query("Select body from users limit 11")
defer rows.Close()
if err != nil {
// handle this error better than this
log.Fatal(err)
//return
}
var user Users
for rows.Next() {
rows.Scan(&user.ID, &user.Subject, &user.Phone)
users = append(users, user)
}
for rows1.Next() {
rows1.Scan(&user.Body)
users = append(users, user)
}
return
}
I have a table called users which has no primary key, basically:
user_id . name . body
-----------------------
1 . model . 2
1 . brand . 1
1 . fuel . 3
1 . date . 1
1 . year . 1
I have to have a result:
userid . model . brand . fuel . date . year
1 . 2 . 1 . 3 . 1 . 1
so the values in the column name gonna be as rows. I have already defined my struct which contains all the fields needed.

Answer 1

Looking at the example code it's clear that you should do whatever you're doing in one query instead of two. Even if your real code is a little different, say you need to query more than one table, you should still probably do only one query using JOINs.
users := make([]*User, 0)
rows, err := db1.Query("SELECT user_id, subject,phone, body FROM users limit 11")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
for rows.Next() {
user := new(User)
if err := rows.Scan(&user.ID, &user.Subject, &user.Phone, &user.Body); err != nil {
panic(err)
}
users = append(users, user)
}
if err := rows.Err(); err != nil {
panic(err)
}
That said, if you want to do it the way you illustrated in your question you can do that like this.
(this probably not what you should do)
users := make([]*User, 0)
rows, err := db1.Query("SELECT user_id, subject,phone FROM users limit 11")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
rows1, err := db1.Query("Select body from users limit 11")
if err != nil {
panic(err)
}
defer rows1.Close()
for rows.Next() {
user := new(User)
if err := rows.Scan(&user.ID, &user.Subject, &user.Phone); err != nil {
panic(err)
}
if !rows1.Next() {
panic("no next body row")
}
if err := rows1.Scan(&user.Body); err != nil {
panic(err)
}
users = append(users, user)
}
if err := rows.Err(); err != nil {
panic(err)
}
if err := rows1.Err(); err != nil {
panic(err)
}

Answer 2

const maxPerPage = 100
type Scanable interface {
GetScans() []interface{}
}
type User struct {
ID int
Subject string
Phone string
Body string
}
func (s *User) GetScans() []interface{} {
return []interface{}{&s.ID, &s.Subject, &s.Phone, &s.Body}
}
func getNewUserList() []*User {
users := make([]*User, maxPerPage)
for i := 0; i < maxPerPage; i++ {
users[i] = new(User)
}
return users
}
var usersPool = sync.Pool{
New: func() interface{} {
return getNewUserList()
},
}
func getUsers() (b []*User) {
ifc := usersPool.Get()
if ifc != nil {
b = ifc.([]*User)
} else {
b = getNewUserList()
}
return
}
func putUsers(b []*User) {
// if cap(b) <= maxPerPage {
// b = b[:0] // reset
// usersPool.Put(&b)
// }
usersPool.Put(&b)
}
func TestUsers(t *testing.T) {
users := getUsers()
rows, err := PostgresConnection.Query("SELECT user_id, subject,phone, body FROM users limit 11")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
length := 0
for rows.Next() {
if err := rows.Scan(users[i].GetScans()...); err != nil {
panic(err)
}
if err := rows.Err(); err != nil {
panic(err)
}
length++
}
result := users[:length]
fmt.Println(result)
putUsers(users)
}

Answer 3

this is the sample function to get multiple document from db using golang sqlx library.
func GetDocuments() ([]SupportedDocument, error) {
var documents []SupportedDocument
query := `SELECT * FROM documents limit 10`
err := database.Select(&documents, query)
return documents, err
}