Merge pull request #38 from github/rankOne

add a query for finding rank[1]

ql/src/queries/style/RankOne.ql

@@ -0,0 +1,16 @@
+/**
+ * @name Selecting minimum element using `rank[1]`
+ * @description Selecting the minimum element using `rank[1](..)` performs worse than doing the same thing with `min(..)`.
+ * @kind problem
+ * @problem.severity warning
+ * @id ql/rank-one
+ * @tags performance,
+ *       maintainability
+ * @precision very-high
+ */
+
+import ql
+
+from Rank r
+where r.getRankExpr().(Integer).getValue() = 1
+select r, "Using rank[1](..) is an anti-pattern, use min(..) instead."