init simple tutorial with postgis

postgis/work/cities/README.md

@@ -0,0 +1,4 @@
+# Cities
+
+https://dev.to/dm8ry/postgresql-how-to-calculate-the-distance-between-two-cities-based-on-their-corresponding-gps-data-23cm
+

postgis/work/cities/populate.sql

@@ -0,0 +1,16 @@
+CREATE TABLE cities (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(100),
+    latitude NUMERIC,
+    longitude NUMERIC
+);
+
+INSERT INTO cities (name, latitude, longitude) VALUES ('Lisbon', 38.724874, -9.139604);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Porto', 41.158389, -8.629163);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Sintra', 38.800306, -9.379136);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Obidos', 39.362068, -9.157140);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Coimbra', 40.211491, -8.429200);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Covilha', 40.282650, -7.503260);
+INSERT INTO cities (name, latitude, longitude) VALUES ('Fatima', 39.617207, -8.652142);
+
+

postgis/work/cities/query.sql

@@ -0,0 +1,28 @@
+SELECT ST_DistanceSphere(
+    ST_MakePoint(city1.longitude, city1.latitude),
+    ST_MakePoint(city2.longitude, city2.latitude)
+) / 1000 AS distance_in_km
+FROM cities AS city1
+CROSS JOIN cities AS city2
+WHERE city1.name = 'Lisbon'
+  AND city2.name = 'Porto';
+
+SELECT ST_DistanceSphere(
+    ST_MakePoint(city1.longitude, city1.latitude),
+    ST_MakePoint(city2.longitude, city2.latitude)
+) / 1000 AS distance_in_km
+FROM cities AS city1
+CROSS JOIN cities AS city2
+WHERE city1.name = 'Sintra'
+  AND city2.name = 'Coimbra';
+
+SELECT city1.name "from", city2.name "to", round(ST_DistanceSphere(
+    ST_MakePoint(city1.longitude, city1.latitude),
+    ST_MakePoint(city2.longitude, city2.latitude)
+) / 1000) AS distance_in_km
+FROM cities AS city1
+CROSS JOIN cities AS city2
+where city1.name > city2.name
+order by 3 desc, 1, 2;
+
+