Change return type after eval to the right type

Signed-off-by: Juanjo Alvarez <juanjo@sourced.tech>

sql/expression/function/greatest_least.go

@@ -16,6 +16,7 @@ import (
 // are mixed with non numerically convertible strings, those are ignored.
 type Greatest struct {
 	Args []sql.Expression
+	returnType sql.Type
 }
 
 // ErrUnsupportedType is returned when an argument to Greatest or Latest is not numeric or string
@@ -33,11 +34,11 @@ func NewGreatest(args ...sql.Expression) (sql.Expression, error) {
 		}
 	}
 
-	return &Greatest{args}, nil
+	return &Greatest{args, sql.Float64}, nil
 }
 
 // Type implements the Expression interface.
-func (f *Greatest) Type() sql.Type { return sql.Float64 }
+func (f *Greatest) Type() sql.Type { return f.returnType }
 
 // IsNullable implements the Expression interface.
 func (f *Greatest) IsNullable() bool {
@@ -154,12 +155,15 @@ func (f *Greatest) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	}
 
 	if allInt {
+		f.returnType = sql.Int64
 		return int64(greatestNum), nil
 	} else if allString {
+		f.returnType = sql.Text
 		return greatestString, nil
 	}
 
 	// float64
+	f.returnType = sql.Float64
 	return greatestNum, nil
 }
 
@@ -170,6 +174,7 @@ func (f *Greatest) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 // are mixed with non numerically convertible strings, those are ignored.
 type Least struct {
 	Args []sql.Expression
+	returnType sql.Type
 }
 
 // NewLeast creates a new Least UDF
@@ -188,11 +193,11 @@ func NewLeast(args ...sql.Expression) (sql.Expression, error) {
 		}
 	}
 
-	return &Least{args}, nil
+	return &Least{args, sql.Float64}, nil
 }
 
 // Type implements the Expression interface.
-func (f *Least) Type() sql.Type { return sql.Float64 }
+func (f *Least) Type() sql.Type { return f.returnType }
 
 // IsNullable implements the Expression interface.
 func (f *Least) IsNullable() bool {
@@ -309,11 +314,14 @@ func (f *Least) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	}
 
 	if allInt {
+		f.returnType = sql.Int64
 		return int64(leastNum), nil
 	} else if allString {
+		f.returnType = sql.Text
 		return leastString, nil
 	}
 
 	// float
+	f.returnType = sql.Float64
 	return leastNum, nil
 }

sql/expression/function/greatest_least_test.go

@@ -8,6 +8,18 @@ import (
 )
 
 func TestGreatest(t *testing.T) {
+
+	// XXX
+	//table := mem.NewTable("foo", sql.Schema{
+	//	{Name: "str_no_num", Type: sql.Text, Source: "foo"},
+	//	{Name: "str_num1", Type: sql.Text, Source: "foo"},
+	//	{Name: "str_num9", Type: sql.Text, Source: "foo"},
+	//	{Name: "int1", Type: sql.Int64, Source: "foo"},
+	//	{Name: "int5", Type: sql.Int64, Source: "foo"},
+	//	{Name: "float2", Type: sql.Float64, Source: "foo"},
+	//	{Name: "float9", Type: sql.Float64, Source: "foo"},
+	//})
+
 	testCases := []struct {
 		name string
 		args []sql.Expression