如何在不知道列的情况下从表读取行到地图

Question

In my golang app i need to do SQL query to MySQL to get single row and put result in a map[string]string keys are column names.

But i don't know what will be columns. Query is like

SELECT * FROM mytable

I use "database/sql" .

I found only Scan function

db.QueryRow("SELECT * FROM mytable").Scan(&var1, &var2,...)

but this doesn't work for my condition. I don't know how many variables will be there. And also I need column names.

Is it possible to do with database/sql ?

Update. I found how to solve part of this problem. How to get column names from a result set.

rows, err := db.Query(sqlcommand)

cols, err := rows.Columns()

So, i can use to make keys for a map. But i still don't know how to get values. Because, values can have different type.

data = make(map[string]string)

if rows.Next() {
    columns := make([]interface{}, len(cols))
    columnPointers := make([]interface{}, len(cols))
    for i, _ := range columns {
        columnPointers[i] = &columns[i]
    }

    err = rows.Scan(columnPointers...)

    for i, colName := range cols {
        // value is in columns[i] of interface type.
        // How to extract it from here? 
        // ....
        data[colName] = val
    }
}

P.S. This question is not duplicate of "Get table column names in mysql? ". I wanted to get columns of returned data set, not just a table.

Answer 1

You seem to be on the right track. According to the definition of Rows.Scan, you can supply values of the desired destination type, which would be string here. So changing the type of columns to []string should work:

var db sql.DB
var sqlcommand string

rows, _ := db.Query(sqlcommand)
cols, _ := rows.Columns()

data := make(map[string]string)

if rows.Next() {
    columns := make([]string, len(cols))
    columnPointers := make([]interface{}, len(cols))
    for i, _ := range columns {
        columnPointers[i] = &columns[i]
    }

    rows.Scan(columnPointers...)

    for i, colName := range cols {
        data[colName] = columns[i]
    }
}