added ColumnAlias

[derkan]

Hi Sam,

Given dummies table with column ATextnamed asa_text`:

type DummyAlias struct {
	ID              int            `db:"id,key,auto"`
	AText           string         `db:"new_name"`
}
singleDummy := DummyAlias{}
selectStmt := db.SelectFrom("dummies").
	Where("an_integer = ?", 13)
selectStmt.ColumnAlias("a_text", "new_name")
selectStmt.OrderBy("new_name")

In the result set column will be named as new_name.

OK. Why I need this?

When joinin tables, aliased table columns becomes weird. For following if ColumnAlias is not used, tag for AuthorName shoul be db:"a.name". And at result rows, column name will be also a.name.

type BookNamed struct {
	Book `db:",rel=b" json:""`   // Embeeding book struct
	AuthorName string `db:"author_name" json:"author_name"` 
}
q := db.SelectFrom("books as b").InnerJoin("authors","a",godb.Q("b.author_id=a.id"))
q.ColumnAlias("a.name", "author_name")

The result will be more convenient for SQL producing

  SELECT b.*, a.name as author_name
    FROM books as b
    JOIN authors as a ON b.author_id = a.id
ORDER BY author_name

Regards,
Erkan.