Rows.Scan fails with Scanner objects, but Row.Scan works ok with Scanner objects. about mysql

[Fung-Chai]

Using the delve debugger, I dug into the go-sql-driver code and discovered that Row.Scan calls binaryRows.Next and Rows.Scan calls textRows.Next. This explains why QueryRow returns the correct types but Query returns []uint8 for all columns. The question now is why Rows.Scan doesn't call binaryRows.Next as well. I will dig on.

[Fung-Chai]

Another discovery.

My original code, which makes use of Query produces the wrong results.

// Query will call the go-sql-driver's textRows.Next function, which presents []uint8 (strings) to all the scanners.
rows, err := db.Query("select * from fruits;")
// err is nil
defer rows.Close()
for rows.Next() {
        err := rows.Scan(id_scanner, name_scanner, year_scanner, amount_scanner, price_scanner)
        // err is nil, but output is wrong
}

But I can get the right output with Prepare, calling Query via the statement object.

statement, err := db.Prepare("select * from fruits;")
// err is ni
rows, err := statement.Query()
// err is nil
defer rows.Close()
for rows.Next() {
        err := rows.Scan(id_scanner, name_scanner, year_scanner, amount_scanner, price_scanner)
        // err is nil, and output is the same as that produced by Row.Scan
}

The mysqlConn.queyy returns textRows while mysqlStmt.query returns *binaryRows.

[methane]

Using placeholder makes your query binary.
When implementing Scanner, you should expect many driver.Value type input, not single consistent one.

See #1452 for mitigations implemented in next release.