将int数组转换为以'，'分隔的字符串

Question

I know that for string array []string I can use strings.Join(a []string, ',') but I want to do the same thing for an integer array []int.

My usecase is something like this for a query where variants is []map[string]int

 var Ids []int
    sqlStr := "select id from mapping where my_id in ("
    for _, mp := range variants {
       sqlStr += "?,"
       Ids = append(Ids, mp["id"])
    }
    sqlStr = strings.TrimRight(sqlStr, ",")
    rows, err := db.Query(sqlStr+")", strings.Join(Ids, ',')) // I can't do this because Join needs String array

How to achieve this?

Answer 1

Here is an efficient way to do that:

func sqlIntSeq(ns []int) string {
    if len(ns) == 0 {
        return ""
    }

    // Appr. 3 chars per num plus the comma.
    estimate := len(ns) * 4
    b := make([]byte, 0, estimate)
    // Or simply
    //   b := []byte{}
    for _, n := range ns {
        b = strconv.AppendInt(b, int64(n), 10)
        b = append(b, ',')
    }
    b = b[:len(b)-1]
    return string(b)
}

You can use it in the SQL queries like that:

query := `SELECT * FROM table WHERE id IN (` + sqlIntSeq(ids) + `)`

Playground: https://play.golang.org/p/zi7YYetGu7.