Update useful-snippets.md

docs/useful-snippets.md

@@ -2,32 +2,50 @@
 
 ## Database queries
 
-### Query current states for all labels
+### Number of labels in each state
+```
+SELECT latest_states.new_state, COUNT(*) AS num_labels_in_state
+FROM (
+	SELECT history.label_name, history.new_state
+	FROM history
+	JOIN (
+		SELECT label_name, MAX(id) AS max_id
+		FROM history
+		GROUP BY label_name
+	) states
+	ON
+		history.id = states.max_id AND
+		history.label_name = states.label_name
+) latest_states
+GROUP BY latest_states.new_state;
+```
+
+### Latest state for all labels
 ```
 SELECT history.label_name, history.created, history.new_state
 FROM history
 JOIN (
-	SELECT label_name, MAX(created) AS max_created
+	SELECT label_name, MAX(id) AS max_id
 	FROM history
 	GROUP BY label_name
 ) latest_states
 ON
-	history.created = latest_states.max_created AND
+	history.id = latest_states.max_id AND
 	history.label_name = latest_states.label_name;
 ```
 
-### Count number of labels in a specific state
+### Number of labels in a specific state
 
 ```
 SELECT COUNT(*)
 FROM history
 JOIN (
-	SELECT label_name, MAX(created) AS max_created
+	SELECT label_name, MAX(id) AS max_id
 	FROM history
 	GROUP BY label_name
 ) latest_states
 ON
-	history.created = latest_states.max_created AND
+	history.id = latest_states.max_id AND
 	history.label_name = latest_states.label_name
 WHERE history.new_state = 'STATE_NAME';
 ```