Type        JoinType
	Association string
	Subquery    Expression
	Table       string
}

func Has(name string) JoinTarget {
	return JoinTarget{Type: InnerJoin, Association: name}
}

func (jt JoinType) Association(name string) JoinTarget {
	return JoinTarget{Type: jt, Association: name}
}

func (jt JoinType) AssociationFrom(name string, subquery Expression) JoinTarget {

type ViewOption struct {
	Replace     bool   // If true, exec `CREATE`. If false, exec `CREATE OR REPLACE`
	CheckOption string // optional. e.g. `WITH [ CASCADED | LOCAL ] CHECK OPTION`
	Query       *DB    // required subquery.
}

// ColumnType column type interface
type ColumnType interface {
	Name() string
	DatabaseTypeName() string                 // varchar
	ColumnType() (columnType string, ok bool) // varchar(64)