sql/(parse,expression): implement unary minus

erizocosmico · erizocosmico · commit 452abbfb0413 · 2018-10-16T11:58:26.000+02:00
Signed-off-by: Miguel Molina &lt;miguel@erizocosmi.co&gt;
diff --git a/engine_test.go b/engine_test.go
@@ -418,6 +418,10 @@ var queries = []struct {
 			{"c", int32(0)},
 		},
 	},
+	{
+		`SELECT -1`,
+		[]sql.Row{{int64(-1)}},
+	},
 }
 
 func TestQueries(t *testing.T) {
diff --git a/sql/expression/arithmetic.go b/sql/expression/arithmetic.go
@@ -2,6 +2,7 @@ package expression
 
 import (
 	"fmt"
+	"reflect"
 
 	errors "gopkg.in/src-d/go-errors.v1"
 	"gopkg.in/src-d/go-vitess.v1/vt/sqlparser"
@@ -407,3 +408,81 @@ func mod(lval, rval interface{}) (interface{}, error) {
 
 	return nil, errUnableToCast.New(lval, rval)
 }
+
+// UnaryMinus is an unary minus operator.
+type UnaryMinus struct {
+	UnaryExpression
+}
+
+// NewUnaryMinus creates a new UnaryMinus expression node.
+func NewUnaryMinus(child sql.Expression) *UnaryMinus {
+	return &UnaryMinus{UnaryExpression{Child: child}}
+}
+
+// Eval implements the sql.Expression interface.
+func (e *UnaryMinus) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	child, err := e.Child.Eval(ctx, row)
+	if err != nil {
+		return nil, err
+	}
+
+	if child == nil {
+		return nil, nil
+	}
+
+	if !sql.IsNumber(e.Child.Type()) {
+		child, err = sql.Float64.Convert(child)
+		if err != nil {
+			child = 0.0
+		}
+	}
+
+	switch n := child.(type) {
+	case float64:
+		return -n, nil
+	case float32:
+		return -n, nil
+	case int64:
+		return -n, nil
+	case uint64:
+		return -int64(n), nil
+	case int32:
+		return -n, nil
+	case uint32:
+		return -int32(n), nil
+	default:
+		return nil, sql.ErrInvalidType.New(reflect.TypeOf(n))
+	}
+}
+
+// Type implements the sql.Expression interface.
+func (e *UnaryMinus) Type() sql.Type {
+	typ := e.Child.Type()
+	if !sql.IsNumber(typ) {
+		return sql.Float64
+	}
+
+	if typ == sql.Uint32 {
+		return sql.Int32
+	}
+
+	if typ == sql.Uint64 {
+		return sql.Int64
+	}
+
+	return e.Child.Type()
+}
+
+func (e *UnaryMinus) String() string {
+	return fmt.Sprintf("-%s", e.Child)
+}
+
+// TransformUp implements the sql.Expression interface.
+func (e *UnaryMinus) TransformUp(f sql.TransformExprFunc) (sql.Expression, error) {
+	c, err := e.Child.TransformUp(f)
+	if err != nil {
+		return nil, err
+	}
+
+	return f(NewUnaryMinus(c))
+}
diff --git a/sql/expression/arithmetic_test.go b/sql/expression/arithmetic_test.go
@@ -360,3 +360,31 @@ func TestAllInt64(t *testing.T) {
 		})
 	}
 }
+
+func TestUnaryMinus(t *testing.T) {
+	testCases := []struct {
+		name     string
+		input    interface{}
+		typ      sql.Type
+		expected interface{}
+	}{
+		{"int32", int32(1), sql.Int32, int32(-1)},
+		{"uint32", uint32(1), sql.Uint32, int32(-1)},
+		{"int64", int64(1), sql.Int64, int64(-1)},
+		{"uint64", uint64(1), sql.Uint64, int64(-1)},
+		{"float32", float32(1), sql.Float32, float32(-1)},
+		{"float64", float64(1), sql.Float64, float64(-1)},
+		{"int text", "1", sql.Text, float64(-1)},
+		{"float text", "1.2", sql.Text, float64(-1.2)},
+		{"nil", nil, sql.Text, nil},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			f := NewUnaryMinus(NewLiteral(tt.input, tt.typ))
+			result, err := f.Eval(sql.NewEmptyContext(), nil)
+			require.NoError(t, err)
+			require.Equal(t, tt.expected, result)
+		})
+	}
+}
diff --git a/sql/parse/parse.go b/sql/parse/parse.go
@@ -737,6 +737,8 @@ func exprToExpression(e sqlparser.Expr) (sql.Expression, error) {
 
 	case *sqlparser.BinaryExpr:
 		return binaryExprToExpression(v)
+	case *sqlparser.UnaryExpr:
+		return unaryExprToExpression(v)
 	}
 }
 
@@ -882,6 +884,21 @@ func selectExprToExpression(se sqlparser.SelectExpr) (sql.Expression, error) {
 	}
 }
 
+func unaryExprToExpression(e *sqlparser.UnaryExpr) (sql.Expression, error) {
+	switch e.Operator {
+	case sqlparser.MinusStr:
+		expr, err := exprToExpression(e.Expr)
+		if err != nil {
+			return nil, err
+		}
+
+		return expression.NewUnaryMinus(expr), nil
+
+	default:
+		return nil, ErrUnsupportedFeature.New("unary operator: " + e.Operator)
+	}
+}
+
 func binaryExprToExpression(be *sqlparser.BinaryExpr) (sql.Expression, error) {
 	switch be.Operator {
 	case
