GRDB in Swift - .fetchAll Only Ever Returns One Column

Original Swift Code

func getUserByEmpNum(_ id: Int) -> String {
    let nameQuery: String = "SELECT fld_str_firstname, fld_str_lastName FROM userView WHERE fld_int_id = \(id);"

    var returnStr = ""
    do {
        let dbQueue = try DatabaseQueue(path: MYCDatabase.pathToDatabase)
        try dbQueue.inTransaction(.none) { (db) -> Database.TransactionCompletion in
            let returnStrs = try String.fetchAll(db, sql: nameQuery)
            // Breakpoint set here shows returnStrs only has one element.
            return .commit
        }
    } catch {
        print(error)
    }

    return returnStr
}

Problem Description

When executing a query that retrieves a single column, such as:

SELECT fld_str_firstname FROM userView WHERE fld_int_id = 2;

the resulting returnStrs array correctly contains a single element.

However, when I select multiple columns, as in the original query:

SELECT fld_str_firstname, fld_str_lastName FROM userView WHERE fld_int_id = 2;

I still only receive one string element in returnStrs.

My Questions

Why does fetching multiple columns in SwiftGRDB result in only one string?
How should I modify my code to correctly retrieve and access all selected columns separately?

Additional Information

SwiftGRDB is the library being used.
Placing a breakpoint and inspecting returnStrs confirms only a single element is returned, despite multiple columns being queried.

Solution

String.fetchAll returns an array of Strings extracted from the leftmost selected column, as documented. One string for each fetched row. Not one string for each selected column.

If you want to grab strings from several columns, use Row.fetchAll, which returns an array of database rows. From those rows, you can extract each column you are interested into:

let rows = try Row.fetchAll(db, sql: "SELECT fld_str_firstname, fld_str_lastName FROM ...")
for row in rows {
    let firstName: String = row["fld_str_firstname"]
    let lastName: String = row["fld_str_lastName"]
}

See this chapter of the documentation for more information about extracting values from database rows.

Since you are reading the name from a single row identified with its id, you may prefer the fetchOne method, which consumes a single database row (see Fetching Methods):

if let row = try Row.fetchOne(db, sql: "SELECT ... WHERE fld_int_id = ?", arguments: [id]) {
    let firstName: String = row["fld_str_firstname"]
    let lastName: String = row["fld_str_lastName"]
    // Use first and last name 
} else {
    // ID does not exist in the database: do what is appropriate.
}