mysql: add weather-observation-station-12

mysql/weather-observation-station-12/solution.sql

@@ -0,0 +1,6 @@
+SET @vowels = 'a,e,i,o,u';
+
+SELECT DISTINCT CITY
+FROM STATION
+WHERE NOT FIND_IN_SET(LEFT(CITY, 1), @vowels)
+AND NOT FIND_IN_SET(RIGHT(CITY, 1), @vowels);