func (this *Column) Key() *Column {
	this.key = true
	this.table.addKey(this)
	return this
}
set this as a key column

return
package db
import (
	tk "github.com/quintans/toolkit"
	"strings"
)
type Column struct {
	table     *Table  
	name      string  
	alias     string  
	key       bool
	mandatory bool
	version   bool
	deletion  bool
	hash      int
}
func (this *Column) As(alias string) *Column {
	this.alias = alias
	return this
}
func (this *Column) For(tableAlias string) *ColumnHolder {
	return NewColumnHolder(this).For(tableAlias)
}