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

Reading "SELECT *" Columns into []string in Go

In the database world, fetching data from a table using a "SELECT " query is a common practice, but in the world of programming, manually working with such data can be cumbersome. This article aims to simplify the process of reading "SELECT " query results into a []string slice in Go, leveraging the robust Go standard library.

When dealing with a table with an unknown number of columns and data types, the challenge lies in capturing the data into a structured form. The Scan method provided by Rows allows you to fill specific data types into pre-defined variables, but it doesn't offer a direct way to read into a []string.

To overcome this, we employ a technique that creates an []interface{} slice, where each element is a pointer to a string in the []string slice. This bridging step allows the Scan method to fill the interface slice, which can then be easily converted into the desired []string.

Here's a revised version of the example code provided in the question:

func dumpTable(rows *sql.Rows, out io.Writer) error {
    colNames, err := rows.Columns()
    if err != nil {
        return err
    }
    writer := csv.NewWriter(out)
    writer.Comma = '\t'
    readCols := make([]interface{}, len(colNames))
    writeCols := make([]string, len(colNames))
    for i, _ := range writeCols {
        readCols[i] = &writeCols[i]
    }
    for rows.Next() {
        err := rows.Scan(readCols...)
        if err != nil {
            return err
        }
        writer.Write(writeCols)
    }
    if err = rows.Err(); err != nil {
        return err
    }
    writer.Flush()
    return nil
}

This solution seamlessly bridges the gap between the Scan method and the []string, allowing you to store the "SELECT *" query results into a structured and usable format.

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