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POread "SELECT *" columns into []string in go
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copied!<p>I want to write a Go program to dump rows from from a database table into a csv file using <code>SELECT *</code>.</p> <p>Go provides the excellent <a href="http://golang.org/pkg/database/sql" rel="noreferrer">sql</a> and <a href="http://golang.org/pkg/encoding/csv/" rel="noreferrer">csv</a> apis, but <code>csv</code> expects arrays of strings and the <code>Scan</code> method in <code>Rows</code> "fills" fields according to their types. As I don't know the table before, I have no idea how many columns there are and what their types are.</p> <p>It's my first program in Go, so I'm struggling a little.</p> <p>How do I best read the columns from a <code>Rows</code> instance into a <code>[]string</code> - and is that the "right" way?</p> <p>Thanks!</p> <p><strong>UPDATE</strong></p> <p>I'm still struggling with the parameters. This is my code, for now I'm using <code>panic</code> instead of returning an <code>error</code>, but I'm going to change that later. In my test, I'm passing the query result and <code>os.Stdout</code>.</p> <pre><code>func dumpTable(rows *sql.Rows, out io.Writer) error { colNames, err := rows.Columns() if err != nil { panic(err) } if rows.Next() { writer := csv.NewWriter(out) writer.Comma = '\t' cols := make([]string, len(colNames)) processRow := func() { err := rows.Scan(cols...) if err != nil { panic(err) } writer.Write(cols) } processRow() for rows.Next() { processRow() } writer.Flush() } return nil } </code></pre> <p>For this, I get <code>cannot use cols (type []string) as type []interface {} in function argument</code> (at the <code>writer.Write(cols)</code> line.</p> <p>I then tested</p> <pre><code> readCols := make([]interface{}, len(colNames)) writeCols := make([]string, len(colNames)) processRow := func() { err := rows.Scan(readCols...) if err != nil { panic(err) } // ... CONVERSION? writer.Write(writeCols) } </code></pre> <p>which lead to <code>panic: sql: Scan error on column index 0: destination not a pointer</code>.</p> <p><strong>UPDATE 2</strong></p> <p>I independently arrived at <a href="https://stackoverflow.com/users/694331/anisus">ANisus</a>' solution. This is the code I'm using now.</p> <pre><code>func dumpTable(rows *sql.Rows, out io.Writer) error { colNames, err := rows.Columns() if err != nil { panic(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 { panic(err) } writer.Write(writeCols) } if err = rows.Err(); err != nil { panic(err) } writer.Flush() return nil } </code></pre>

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