update or add IsNullable implementation for log and math functions

Author: angelamayxie

sql/expression/function/logarithm.go

@@ -112,7 +112,7 @@ func (*LogBase) CollationCoercibility(ctx *sql.Context) (collation sql.Collation
 
 // IsNullable implements the sql.Expression interface.
 func (l *LogBase) IsNullable() bool {
-	return l.base == float64(1) || l.base <= float64(0) || l.Child.IsNullable()
+	return true
 }
 
 // Eval implements the Expression interface.
@@ -196,7 +196,7 @@ func (*Log) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID,
 
 // IsNullable implements the Expression interface.
 func (l *Log) IsNullable() bool {
-	return l.LeftChild.IsNullable() || l.RightChild.IsNullable()
+	return true
 }
 
 // Eval implements the Expression interface.

sql/expression/function/math.go

@@ -268,6 +268,11 @@ func (*Tan) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID,
 	return sql.Collation_binary, 5
 }
 
+// IsNullable implements sql.Expression
+func (t *Tan) IsNullable() bool {
+	return true
+}
+
 // Eval implements sql.Expression
 func (t *Tan) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	val, err := t.EvalChild(ctx, row)
@@ -325,6 +330,11 @@ func (*Asin) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID,
 	return sql.Collation_binary, 5
 }
 
+// IsNullable implements sql.Expression
+func (a *Asin) IsNullable() bool {
+	return true
+}
+
 // Eval implements sql.Expression
 func (a *Asin) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	val, err := a.EvalChild(ctx, row)
@@ -382,6 +392,11 @@ func (*Acos) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID,
 	return sql.Collation_binary, 5
 }
 
+// IsNullable implements sql.Expression
+func (a *Acos) IsNullable() bool {
+	return true
+}
+
 // Eval implements sql.Expression
 func (a *Acos) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	val, err := a.EvalChild(ctx, row)
@@ -559,6 +574,11 @@ func (*Cot) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID,
 	return sql.Collation_binary, 5
 }
 
+// IsNullable implements sql.Expression
+func (c *Cot) IsNullable() bool {
+	return true
+}
+
 // Eval implements sql.Expression
 func (c *Cot) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	val, err := c.EvalChild(ctx, row)
@@ -991,6 +1011,11 @@ func (e *Exp) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID
 	return sql.Collation_binary, 5
 }
 
+// IsNullable implements sql.Expression
+func (e *Exp) IsNullable() bool {
+	return true
+}
+
 // Eval implements the Expression interface.
 func (e *Exp) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	if e.Child == nil {