Add example if not exists for FROM/JOIN AS

[kokizzu]

Is your feature request related to a problem? Please describe.
for example query:

WITH a AS (
   SELECT x, y, COUNT(z) zcount
   FROM a
   GROUP BY 1,2
)
SELECT x, sender.name, spouse.name, COUNT(y), MAX(zcount)
FROM a
  LEFT JOIN users AS sender ON a.x = users.id
  LEFT JOIN users AS spouse ON users.spouse_id = spouse.id
GROUP BY 1,2,3

Describe the solution you'd like

sender := Users.AS("sender")
spouse := Users.AS("spouse")

// later can be like this
FROM(
  cteA.
    LEFT_JOIN(sender,xCol.EQ(sender.Id).
    LEFT_JOIN(spouse,sender.SpouseId.EQ(spouse.Id)
)

[go-jet]

Hi @kokizzu, take a look at self join, with statement and sub query.
Psudo like code should look something like:

a := CTE("a")
// export columns from 'a' cte
aX := A.X.From(a)
aY := A.Y.From(a)
aZcount := IntegerColumn("zcount").From(a)

sender := Users.AS("sender")
spouse := Users.AS("spouse")

stmt := WITH(
	a.AS(
		SELECT(
			A.X,
			A.Y,
			COUNT(A.Z).AS("zcount"),
		).FROM(
			A,
		).GROUP_BY(
			A.X,
			A.Y,
		),
	),
)(
	SELECT(
		ax.AS("x"),
		sender.Name.AS("sender_name"),
		spouse.Name.AS("spouse_name"),
		COUNT(aY).AS("count_ay"),
		MAX(aZcount).AS("max_az_count"),
	).FROM(
		a.LEFT_JOIN(sender, aX.EQ(sender.ID)).
		   LEFT_JOIN(spouse, sender.SpouseID.EQ(spouse.ID)),
	).GROUP_BY(
		ax,
		sender.Name,
		spouse.Name,
	),
)

var dest []struct {
	X          string
	SenderName string
	SpouseName string
	CountAY    int
	MaxAZCount int
}

err := stmt.Query(db, &dest)