sorry Andy,
it seems i haven't read your example carefully enough. your question was
what to do if the query returns multiple rows. i tried to explain that.
however the query in your example looks like it will only ever return a
single row, because you probably marked the username column in your
users table as unique. for that use QueryRow, which is just a convenient
wrapper function for querying a single result row.
you can discover this fact through the documentation. in
https://godoc.org/database/sql#Row you can click on the Scan method name
link to get to the source code of that method
https://golang.org/src/database/sql/sql.go#L3196 and see how it uses
Rows to scan a single result or return the ErrNoRows.
both documentation and source code of the standard library are easy to
discover and read compared to most other languages. i hope this tip
might help you answer other questions yourself as well.
have fun!
On 13.09.20 10:19, Andy Hall wrote:
thanks martin...it seems with no query handling the database Next func
does not run anyway as the rows evaluate to false in the for loop...
// tell other players in the room you have entered
rows_users, err := database.Query("SELECT username FROM users WHERE room
= ? AND username != ?", room, username)
// if the user from the db is connected then send them a message
var user string
for rows_users.Next() {
rows_users.Scan(&user)
if conn, ok := m[user]; ok {
conn.Write([]byte(string(username + " has entered the room\n# ")))
}
}
I should probably print something in the loop to confirm but I certainly
don't get any null pointer connection errors so may just comment this
for clarity and leave it. I guess it saves more code ;-)
On Saturday, September 12, 2020 at 9:53:28 PM UTC+1 mb0 wrote:
hi Andy,
when you take a look at the documentation of the Rows type returned by
Query you will see a helpful example of its common use, appending the
scanned results into a slice. my recommendation would be to follow this
example and then check if the len(slice) == 0 to detect an empty set.
if you don't actually need the results scanned into a go slice,
consider
using query row with a sql select count(*) … query and scan, then check
the resulting integer.
have fun!
On 12.09.20 21:16, Andy Hall wrote:
> the database.Query func does not return ErrNoRows unlike the
> database.QueryRow func so how to I handle an empty set when I
wish to
> run a query which returns multiple rows...
>
> // tell other players in the room you have entered
> rows_users, err := database.Query("SELECT username FROM users
WHERE room
> = ? AND username != ?", room, username)
> // handle an empty set
> if err != nil {
> if err == sql.ErrNoRows {
> fmt.Println("EMPTY SET")
> } else {
> fmt.Println(err)
> return
> }
>
> The string "EMPTY SET" is never printed as the condition is never
> set...so continues to run through the if statement.
>
> Surely there is is way to handle no rows with Query ??
>
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