How to Read SELECT * Columns into a []string in Go?

Complexities of Reading SELECT * Columns into []string in Go

A common task in data processing is to retrieve rows from a database table and store them in a convenient format. In Go, you can use the database/sql package to interface with databases. However, encountering a variable number of columns with unknown types can present a challenge.

The sql.Rows type provides access to the results of a query, but its Scan method expects typed fields to populate. Converting the values into a slice of strings ([]string) directly is not straightforward.

Solution: Utilizing an Interface Slice

To address this issue, you must create an interface slice ([]interface{}) that points to each string in your string slice. This involves allocating a temporary slice and setting each element to point to the corresponding element in the string slice.

Example Code:

rawResult := make([][]byte, len(cols))
result := make([]string, len(cols))

dest := make([]interface{}, len(cols)) // A temporary interface{} slice
for i, _ := range rawResult {
    dest[i] = &rawResult[i] // Put pointers to each string in the interface slice
}

Once the interface slice is prepared, you can use it to scan the rows.

Scanning Rows and Converting to Strings

for rows.Next() {
    err = rows.Scan(dest...)
    if err != nil {
        fmt.Println("Failed to scan row", err)
        return
    }

    for i, raw := range rawResult {
        if raw == nil {
            result[i] = "\N"
        } else {
            result[i] = string(raw)
        }
    }

    fmt.Printf("%#v\n", result)
}

This approach allows you to directly read the column values into a string slice, accommodating the variable number and types of columns.

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