feature #161: add support for recursive CTEs

This change adds support for recursive CTEs by introducing the
`WithRecursive` method, which builds a `WITH RECURSIVE` clause.

Author: arikkfir

cte.go

@@ -13,6 +13,11 @@ func With(tables ...*CTETableBuilder) *CTEBuilder {
 	return DefaultFlavor.NewCTEBuilder().With(tables...)
 }
 
+// WithRecursive creates a new recursive CTE builder with default flavor.
+func WithRecursive(tables ...*CTETableBuilder) *CTEBuilder {
+	return DefaultFlavor.NewCTEBuilder().WithRecursive(tables...)
+}
+
 func newCTEBuilder() *CTEBuilder {
 	return &CTEBuilder{
 		args:      &Args{},
@@ -22,6 +27,7 @@ func newCTEBuilder() *CTEBuilder {
 
 // CTEBuilder is a CTE (Common Table Expression) builder.
 type CTEBuilder struct {
+	recursive        bool
 	tableNames       []string
 	tableBuilderVars []string
 
@@ -49,6 +55,12 @@ func (cteb *CTEBuilder) With(tables ...*CTETableBuilder) *CTEBuilder {
 	return cteb
 }
 
+// WithRecursive sets the CTE name and columns and turns on the RECURSIVE keyword.
+func (cteb *CTEBuilder) WithRecursive(tables ...*CTETableBuilder) *CTEBuilder {
+	cteb.With(tables...).recursive = true
+	return cteb
+}
+
 // Select creates a new SelectBuilder to build a SELECT statement using this CTE.
 func (cteb *CTEBuilder) Select(col ...string) *SelectBuilder {
 	sb := cteb.args.Flavor.NewSelectBuilder()
@@ -73,6 +85,9 @@ func (cteb *CTEBuilder) BuildWithFlavor(flavor Flavor, initialArg ...interface{}
 
 	if len(cteb.tableBuilderVars) > 0 {
 		buf.WriteLeadingString("WITH ")
+		if cteb.recursive {
+			buf.WriteString("RECURSIVE ")
+		}
 		buf.WriteStrings(cteb.tableBuilderVars, ", ")
 	}
 

cte_test.go

@@ -30,6 +30,28 @@ func ExampleWith() {
 	// WITH users (id, name) AS (SELECT id, name FROM users WHERE name IS NOT NULL), devices AS (SELECT device_id FROM devices) SELECT users.id, orders.id, devices.device_id FROM users, devices JOIN orders ON users.id = orders.user_id AND devices.device_id = orders.device_id
 }
 
+func ExampleWithRecursive() {
+	sb := WithRecursive(
+		CTETable("source_accounts", "id", "parent_id").As(
+			UnionAll(
+				Select("p.id", "p.parent_id").
+					From("accounts AS p").
+					Where("p.id = 2"), // Show orders for account 2 and all its child accounts
+				Select("c.id", "c.parent_id").
+					From("accounts AS c").
+					Join("source_accounts AS sa", "c.parent_id = sa.id"),
+			),
+		),
+	).Select("o.id", "o.date", "o.amount").
+		From("orders AS o").
+		Join("source_accounts", "o.account_id = source_accounts.id")
+
+	fmt.Println(sb)
+
+	// Output:
+	// WITH RECURSIVE source_accounts (id, parent_id) AS ((SELECT p.id, p.parent_id FROM accounts AS p WHERE p.id = 2) UNION ALL (SELECT c.id, c.parent_id FROM accounts AS c JOIN source_accounts AS sa ON c.parent_id = sa.id)) SELECT o.id, o.date, o.amount FROM orders AS o JOIN source_accounts ON o.account_id = source_accounts.id
+}
+
 func ExampleCTEBuilder() {
 	usersBuilder := Select("id", "name", "level").From("users")
 	usersBuilder.Where(
@@ -82,3 +104,27 @@ func TestCTEBuilder(t *testing.T) {
 	sql = ctetb.String()
 	a.Equal(sql, "/* table init */ t (a, b) /* after table */ AS (SELECT a, b FROM t) /* after table as */")
 }
+
+func TestRecursiveCTEBuilder(t *testing.T) {
+	a := assert.New(t)
+	cteb := newCTEBuilder()
+	cteb.recursive = true
+	ctetb := newCTETableBuilder()
+	cteb.SQL("/* init */")
+	cteb.With(ctetb)
+	cteb.SQL("/* after with */")
+
+	ctetb.SQL("/* table init */")
+	ctetb.Table("t", "a", "b")
+	ctetb.SQL("/* after table */")
+
+	ctetb.As(Select("a", "b").From("t"))
+	ctetb.SQL("/* after table as */")
+
+	sql, args := cteb.Build()
+	a.Equal(sql, "/* init */ WITH RECURSIVE /* table init */ t (a, b) /* after table */ AS (SELECT a, b FROM t) /* after table as */ /* after with */")
+	a.Assert(args == nil)
+
+	sql = ctetb.String()
+	a.Equal(sql, "/* table init */ t (a, b) /* after table */ AS (SELECT a, b FROM t) /* after table as */")
+}