sql/parse: add support for expression aliases. (src-d#61)

* Add alias parsing support.
* Fix plan.Project so that it calculates schema properly
  when child schema differs in names.

Author: smola

sql/analyzer/analyzer_test.go

@@ -50,6 +50,28 @@ func TestAnalyzer_Analyze(t *testing.T) {
 	assert.Nil(err)
 	assert.Equal(expected, analyzed)
 
+	notAnalyzed = plan.NewProject(
+		[]sql.Expression{
+			expression.NewAlias(
+				expression.NewUnresolvedColumn("i"),
+				"foo",
+			),
+		},
+		plan.NewUnresolvedTable("mytable"),
+	)
+	analyzed, err = a.Analyze(notAnalyzed)
+	expected = plan.NewProject(
+		[]sql.Expression{
+			expression.NewAlias(
+				expression.NewGetField(0, sql.Integer, "i"),
+				"foo",
+			),
+		},
+		table,
+	)
+	assert.Nil(err)
+	assert.Equal(expected, analyzed)
+
 	notAnalyzed = plan.NewProject(
 		[]sql.Expression{expression.NewUnresolvedColumn("i")},
 		plan.NewFilter(

sql/parse/parse.go

@@ -175,6 +175,25 @@ func selectToProject(se sqlparser.SelectExprs, child sql.Node) (*plan.Project, e
 	return plan.NewProject(exprs, child), nil
 }
 
+func exprToExpression(e sqlparser.Expr) (sql.Expression, error) {
+	be, ok := e.(sqlparser.BoolExpr)
+	if ok {
+		return boolExprToExpression(be)
+	}
+
+	c, ok := e.(*sqlparser.ComparisonExpr)
+	if ok {
+		return comparisonExprToExpression(c)
+	}
+
+	v, ok := e.(sqlparser.ValExpr)
+	if ok {
+		return valExprToExpression(v)
+	}
+
+	return nil, errUnsupported(e)
+}
+
 func boolExprToExpression(be sqlparser.BoolExpr) (sql.Expression, error) {
 	switch b := be.(type) {
 	default:
@@ -239,6 +258,7 @@ func valExprToExpression(ve sqlparser.ValExpr) (sql.Expression, error) {
 		//TODO
 		return expression.NewLiteral(nil, sql.Null), nil
 	case *sqlparser.ColName:
+		//TODO: add handling of case sensitiveness.
 		return expression.NewUnresolvedColumn(v.Name.Lowered()), nil
 	}
 }
@@ -251,14 +271,16 @@ func selectExprToExpression(se sqlparser.SelectExpr) (sql.Expression, error) {
 		//TODO: Add support for qualified start.
 		return expression.NewStar(), nil
 	case *sqlparser.NonStarExpr:
-		//TODO: Add support for aliases and functions.
-		cn, ok := e.Expr.(*sqlparser.ColName)
-		if !ok {
-			return nil, errUnsupportedFeature("column aliases or functions")
+		expr, err := exprToExpression(e.Expr)
+		if err != nil {
+			return nil, err
+		}
+
+		if e.As.String() == "" {
+			return expr, nil
 		}
 
-		//TODO: Add support for column qualifiers.
 		//TODO: Handle case-sensitiveness when needed.
-		return expression.NewUnresolvedColumn(cn.Name.Lowered()), nil
+		return expression.NewAlias(expr, e.As.Lowered()), nil
 	}
 }

sql/parse/parse_test.go

@@ -18,6 +18,15 @@ var fixtures = map[string]sql.Node{
 		},
 		plan.NewUnresolvedTable("foo"),
 	),
+	`SELECT foo AS bar FROM foo;`: plan.NewProject(
+		[]sql.Expression{
+			expression.NewAlias(
+				expression.NewUnresolvedColumn("foo"),
+				"bar",
+			),
+		},
+		plan.NewUnresolvedTable("foo"),
+	),
 	`SELECT foo, bar FROM foo WHERE foo = bar;`: plan.NewProject(
 		[]sql.Expression{
 			expression.NewUnresolvedColumn("foo"),

sql/plan/project.go

@@ -7,29 +7,25 @@ import (
 type Project struct {
 	UnaryNode
 	expressions []sql.Expression
-	schema      sql.Schema
 }
 
 func NewProject(expressions []sql.Expression, child sql.Node) *Project {
-	schema := sql.Schema{}
-	childSchema := child.Schema()
-	for _, expr := range expressions {
-		for _, field := range childSchema {
-			if expr.Name() == field.Name {
-				schema = append(schema, field)
-				break
-			}
-		}
-	}
 	return &Project{
 		UnaryNode:   UnaryNode{child},
 		expressions: expressions,
-		schema:      schema,
 	}
 }
 
 func (p *Project) Schema() sql.Schema {
-	return p.schema
+	var s sql.Schema
+	for _, e := range p.expressions {
+		f := sql.Field{
+			Name: e.Name(),
+			Type: e.Type(),
+		}
+		s = append(s, f)
+	}
+	return s
 }
 
 func (p *Project) Resolved() bool {

sql/plan/project_test.go

@@ -46,5 +46,16 @@ func TestProject(t *testing.T) {
 	require.Nil(row)
 
 	p = NewProject(nil, child)
-	require.Equal(0, len(p.schema))
+	require.Equal(0, len(p.Schema()))
+
+	p = NewProject([]sql.Expression{
+		expression.NewAlias(
+			expression.NewGetField(1, sql.String, "col2"),
+			"foo",
+		),
+	}, child)
+	schema = sql.Schema{
+		sql.Field{"foo", sql.String},
+	}
+	require.Equal(schema, p.Schema())
 }