Add SUM Aggregation function and fix ignore comma after aggregation f…

…unction

docs/function/aggregations.md

@@ -14,6 +14,13 @@ Accept field name with `NUMBER` to calculate the minimum value of it for all ele
 SELECT name, commit_count, min(commit_count) FROM branches
 ```
 
+### Aggregation `sum`
+The function sum() is an aggregate function that returns the sum of items in a group
+
+```sql
+SELECT name, sum(insertions) FROM diffs GROUP BY name
+```
+
 ### Aggregation `count`
 The function COUNT() is an aggregate function that returns the number of items in a group
 

src/aggregation.rs

@@ -16,6 +16,7 @@ lazy_static! {
         let mut map: HashMap<&'static str, Aggregation> = HashMap::new();
         map.insert("max", aggregation_max);
         map.insert("min", aggregation_min);
+        map.insert("sum", aggregation_sum);
         map.insert("count", aggregation_count);
         map
     };
@@ -38,6 +39,13 @@ lazy_static! {
                 result: DataType::Number,
             },
         );
+        map.insert(
+            "sum",
+            AggregationPrototype {
+                parameter: DataType::Any,
+                result: DataType::Number,
+            },
+        );
         map.insert(
             "count",
             AggregationPrototype {
@@ -73,6 +81,15 @@ fn aggregation_min(field_name: &String, objects: &Vec<GQLObject>) -> String {
     return max_length.to_string();
 }
 
+fn aggregation_sum(field_name: &String, objects: &Vec<GQLObject>) -> String {
+    let mut sum: i64 = 0;
+    for object in objects {
+        let field_value = &object.attributes.get(field_name).unwrap();
+        sum += field_value.parse::<i64>().unwrap();
+    }
+    return sum.to_string();
+}
+
 fn aggregation_count(_field_name: &String, objects: &Vec<GQLObject>) -> String {
     return objects.len().to_string();
 }

src/parser.rs

@@ -322,6 +322,10 @@ fn parse_select_statement(
                     },
                 );
 
+                if tokens[*position].kind == TokenKind::Comma {
+                    *position += 1;
+                }
+
                 continue;
             }
 
@@ -381,6 +385,7 @@ fn parse_select_statement(
     }
 
     if tokens[*position].kind != TokenKind::From {
+        println!("{}", tokens[*position].literal);
         return Err(GQLError {
             message: "Expect `from` keyword after attributes".to_owned(),
             location: tokens[*position].location,