Implement AVG, COUNT, MAX, MIN, SUM functions

parsers/nosql/nosql.peg

@@ -327,6 +327,7 @@ FunctionCall <- StringFunctions
     / TypeCheckingFunctions
     / ArrayFunctions
     / InFunction
+    / AggregateFunctions
 
 StringFunctions <- StringEqualsExpression
     / ToStringExpression
@@ -356,6 +357,12 @@ TypeCheckingFunctions <- IsDefined
     / IsPrimitive
     / IsString
 
+AggregateFunctions <- AvgAggregateExpression
+    / CountAggregateExpression
+    / MaxAggregateExpression
+    / MinAggregateExpression
+    / SumAggregateExpression
+
 ArrayFunctions <- ArrayConcatExpression
     / ArrayLengthExpression
     / ArraySliceExpression
@@ -509,6 +516,26 @@ InFunction <- ex1:SelectProperty ws "IN"i ws "(" ws ex2:SelectItem others:(ws ",
     return createFunctionCall(parsers.FunctionCallIn, append([]interface{}{ex1, ex2}, others.([]interface{})...))
 }
 
+AvgAggregateExpression   <- "AVG"i "(" ws ex:SelectItem  ws ")" {
+    return createFunctionCall(parsers.FunctionCallAggregateAvg, []interface{}{ex})
+}
+
+CountAggregateExpression <- "COUNT"i "(" ws ex:SelectItem ws ")" {
+    return createFunctionCall(parsers.FunctionCallAggregateCount, []interface{}{ex})
+}
+
+MaxAggregateExpression   <- "MAX"i "(" ws ex:SelectItem ws ")" {
+    return createFunctionCall(parsers.FunctionCallAggregateMax, []interface{}{ex})
+}
+
+MinAggregateExpression   <- "MIN"i "(" ws ex:SelectItem ws ")" {
+    return createFunctionCall(parsers.FunctionCallAggregateMin, []interface{}{ex})
+}
+
+SumAggregateExpression   <- "SUM"i "(" ws ex:SelectItem ws ")" {
+    return createFunctionCall(parsers.FunctionCallAggregateSum, []interface{}{ex})
+}
+
 Integer <- [0-9]+ {
     return strconv.Atoi(string(c.text))
 }