Chapter 17 updates

Chapter_17/Chapter_17.sql

@@ -22,6 +22,7 @@ CREATE OR REPLACE VIEW nevada_counties_pop_2019 AS
 
 SELECT *
 FROM nevada_counties_pop_2019
+ORDER BY county_fips
 LIMIT 5;
 
 -- Listing 17-3: Creating a view showing population change for US counties
@@ -33,7 +34,6 @@ CREATE OR REPLACE VIEW county_pop_change_2019_2010 AS
            c2019.county_fips,
            c2019.pop_est_2019 AS pop_2019,
            c2010.estimates_base_2010 AS pop_2010,
-           c2019.pop_est_2019 - c2010.estimates_base_2010 AS raw_change,
            round( (c2019.pop_est_2019::numeric - c2010.estimates_base_2010)
                / c2010.estimates_base_2010 * 100, 1 ) AS pct_change_2019_2010
     FROM us_counties_pop_est_2019 AS c2019
@@ -42,7 +42,7 @@ CREATE OR REPLACE VIEW county_pop_change_2019_2010 AS
         AND c2019.county_fips = c2010.county_fips
         ORDER BY c2019.state_fips, c2019.county_fips;
 
--- Listing 17-4: Selecting columns from the county_pop_change_2010_2000 view
+-- Listing 17-4: Selecting columns from the county_pop_change_2019_2010 view
 
 SELECT county_name,
        state_name,
@@ -50,9 +50,32 @@ SELECT county_name,
        pct_change_2019_2010
 FROM county_pop_change_2019_2010
 WHERE state_name = 'Nevada'
+ORDER BY county_fips
 LIMIT 5;
 
--- Listing 17-5: Creating a view on the employees table
+-- Listing 17-5: Creating a materialized view
+
+DROP VIEW nevada_counties_pop_2019;
+
+CREATE MATERIALIZED VIEW nevada_counties_pop_2019 AS
+    SELECT county_name,
+           state_fips,
+           county_fips,
+           pop_est_2019
+    FROM us_counties_pop_est_2019
+    WHERE state_name = 'Nevada'
+    ORDER BY county_fips;
+
+-- Listing 17-6: Refreshing a materialized view 
+
+REFRESH MATERIALIZED VIEW nevada_counties_pop_2019;
+
+-- Bonus: You can drop a materialized view using:
+-- DROP MATERIALIZED VIEW nevada_counties_pop_2019;
+
+SELECT * FROM employees ORDER BY emp_id;
+
+-- Listing 17-7: Creating a view on the employees table
 
 CREATE OR REPLACE VIEW employees_tax_dept AS
      SELECT emp_id,
@@ -64,9 +87,9 @@ CREATE OR REPLACE VIEW employees_tax_dept AS
      ORDER BY emp_id
      WITH LOCAL CHECK OPTION;
 
-SELECT * FROM employees_tax_dept;
+SELECT * FROM employees_tax_dept ORDER BY emp_id;
--- SELECT * FROM employees;
+
--- Listing 17-6: Successful and rejected inserts via the employees_tax_dept view
+-- Listing 17-8: Successful and rejected inserts via the employees_tax_dept view
 
 INSERT INTO employees_tax_dept (emp_id, first_name, last_name, dept_id)
 VALUES (5, 'Suzanne', 'Legere', 1);
@@ -74,34 +97,35 @@ VALUES (5, 'Suzanne', 'Legere', 1);
 INSERT INTO employees_tax_dept (emp_id, first_name, last_name, dept_id)
 VALUES (6, 'Jamil', 'White', 2);
 
--- optional:
+SELECT * FROM employees_tax_dept ORDER BY emp_id;
-SELECT * FROM employees_tax_dept;
 
-SELECT * FROM employees;
+SELECT * FROM employees ORDER BY emp_id;
 
--- Listing 17-7: Updating a row via the employees_tax_dept view
+-- Listing 17-9: Updating a row via the employees_tax_dept view
 
 UPDATE employees_tax_dept
 SET last_name = 'Le Gere'
 WHERE emp_id = 5;
 
-SELECT * FROM employees_tax_dept;
+SELECT * FROM employees_tax_dept ORDER BY emp_id;
 
 -- Bonus: This will fail because the salary column is not in the view
 UPDATE employees_tax_dept
 SET salary = 100000
 WHERE emp_id = 5;
 
--- Listing 17-8: Deleting a row via the employees_tax_dept view
+-- Listing 17-10: Deleting a row via the employees_tax_dept view
 
 DELETE FROM employees_tax_dept
 WHERE emp_id = 5;
 
 
--- FUNCTIONS
+-- FUNCTIONS AND PROCEDURES
--- https://www.postgresql.org/docs/current/static/plpgsql.html
+-- https://www.postgresql.org/docs/current/sql-createfunction.html
+-- https://www.postgresql.org/docs/current/sql-createprocedure.html
+-- https://www.postgresql.org/docs/current/plpgsql.html
 
--- Listing 17-9: Creating a percent_change function
+-- Listing 17-11: Creating a percent_change function
 -- To delete this function: DROP FUNCTION percent_change(numeric,numeric,integer);
 
 CREATE OR REPLACE FUNCTION
@@ -109,23 +133,26 @@ percent_change(new_value numeric,
                old_value numeric,
                decimal_places integer DEFAULT 1)
 RETURNS numeric AS
-'SELECT round(
+$$
-        ((new_value - old_value) / old_value) * 100, decimal_places
+    SELECT round(
-);'
+            ((new_value - old_value) / old_value) * 100, decimal_places
+    );
+$$
 LANGUAGE SQL
 IMMUTABLE
 RETURNS NULL ON NULL INPUT;
 
--- Listing 17-10: Testing the percent_change() function
+-- Listing 17-12: Testing the percent_change() function
 
 SELECT percent_change(110, 108, 2);
 
--- Listing 17-11: Testing percent_change() on Census data
+-- Listing 17-13: Testing percent_change() on Census data
 
 SELECT c2019.county_name,
        c2019.state_name,
        c2019.pop_est_2019 AS pop_2019,
-       percent_change(c2019.pop_est_2019, c2010.estimates_base_2010) AS pct_chg_func,
+       percent_change(c2019.pop_est_2019,
+                      c2010.estimates_base_2010) AS pct_chg_func,
        round( (c2019.pop_est_2019::numeric - c2010.estimates_base_2010)
            / c2010.estimates_base_2010 * 100, 1 ) AS pct_chg_formula
 FROM us_counties_pop_est_2019 AS c2019
@@ -135,7 +162,7 @@ ON c2019.state_fips = c2010.state_fips
 ORDER BY pct_chg_func DESC
 LIMIT 5;
 
--- Listing 17-12: Adding a column to the teachers table and seeing the data
+-- Listing 17-14: Adding a column to the teachers table and seeing the data
 
 ALTER TABLE teachers ADD COLUMN personal_days integer;
 
@@ -144,52 +171,56 @@ SELECT first_name,
        hire_date,
        personal_days
 FROM teachers;
-SELECT * FROM teachers;
--- Listing 17-13: Creating an update_personal_days() function
 
-CREATE OR REPLACE FUNCTION update_personal_days()
+-- Listing 17-15: Creating an update_personal_days() procedure
-RETURNS void AS $$
+
+CREATE OR REPLACE PROCEDURE update_personal_days()
+LANGUAGE plpgsql
+AS $$
 BEGIN
     UPDATE teachers
     SET personal_days =
-        CASE WHEN (now() - hire_date) BETWEEN '5 years'::interval
+        CASE WHEN (now() - hire_date) >= '10 years'::interval
-                                      AND '10 years'::interval THEN 4
+                  AND (now() - hire_date) < '15 years'::interval THEN 4
-             WHEN (now() - hire_date) > '10 years'::interval THEN 5
+             WHEN (now() - hire_date) >= '15 years'::interval
+                  AND (now() - hire_date) < '20 years'::interval THEN 5
+             WHEN (now() - hire_date) >= '20 years'::interval
+                  AND (now() - hire_date) < '25 years'::interval THEN 6
+             WHEN (now() - hire_date) >= '25 years'::interval THEN 7
              ELSE 3
         END;
     RAISE NOTICE 'personal_days updated!';
-END;
+END
-$$ LANGUAGE plpgsql;
+$$;
 
--- To run the function:
+-- To invoke the procedure:
-SELECT update_personal_days();
+CALL update_personal_days();
 
--- Listing 17-14: Enabling the PL/Python procedural language
+-- Listing 17-16: Enabling the PL/Python procedural language
 
-CREATE EXTENSION plpythonu; -- doesn't work on macOS with PostgresApp
+CREATE EXTENSION plpython3u;
-CREATE EXTENSION plpython3u; -- doesn't work on macOS with PostgresApp
 
--- Listing 17-15: Using PL/Python to create the trim_county() function
+-- Listing 17-17: Using PL/Python to create the trim_county() function
 
 CREATE OR REPLACE FUNCTION trim_county(input_string text)
 RETURNS text AS $$
     import re
     cleaned = re.sub(r' County', '', input_string)
     return cleaned
-$$ LANGUAGE plpythonu;
+$$ LANGUAGE plpython3u;
 
--- Listing 17-16: Testing the trim_county() function
+-- Listing 17-18: Testing the trim_county() function
 
-SELECT geo_name,
+SELECT county_name,
-       trim_county(geo_name)
+       trim_county(county_name)
-FROM us_counties_2010
+FROM us_counties_pop_est_2019
 ORDER BY state_fips, county_fips
 LIMIT 5;
 
 
 -- TRIGGERS
 
--- Listing 17-17: Creating the grades and grades_history tables
+-- Listing 17-19: Creating the grades and grades_history tables
 
 CREATE TABLE grades (
     student_id bigint,
@@ -216,7 +247,7 @@ CREATE TABLE grades_history (
 PRIMARY KEY (student_id, course_id, change_time)
 );  
 
--- Listing 17-18: Creating the record_if_grade_changed() function
+-- Listing 17-20: Creating the record_if_grade_changed() function
 
 CREATE OR REPLACE FUNCTION record_if_grade_changed()
     RETURNS trigger AS
@@ -242,7 +273,7 @@ BEGIN
 END;
 $$ LANGUAGE plpgsql;
 
--- Listing 17-19: Creating the grades_update trigger
+-- Listing 17-21: Creating the grades_update trigger
 
 CREATE TRIGGER grades_update
   AFTER UPDATE
@@ -250,13 +281,13 @@ CREATE TRIGGER grades_update
   FOR EACH ROW
   EXECUTE PROCEDURE record_if_grade_changed();
 
--- Listing 17-20: Testing the grades_update trigger
+-- Listing 17-22: Testing the grades_update trigger
 
 -- Initially, there should be 0 records in the history
 SELECT * FROM grades_history;
 
 -- Check the grades
-SELECT * FROM grades;
+SELECT * FROM grades ORDER BY student_id, course_id;
 
 -- Update a grade
 UPDATE grades
@@ -271,7 +302,7 @@ SELECT student_id,
        new_grade
 FROM grades_history;
 
--- Listing 17-21: Creating a temperature_test table
+-- Listing 17-23: Creating a temperature_test table
 
 CREATE TABLE temperature_test (
     station_name text,
@@ -282,7 +313,7 @@ CREATE TABLE temperature_test (
 PRIMARY KEY (station_name, observation_date)
 );
 
--- Listing 17-22: Creating the classify_max_temp() function
+-- Listing 17-24: Creating the classify_max_temp() function
 -- CHECK AGAINST CATEGORIES USED PREVIOUSLY
 
 CREATE OR REPLACE FUNCTION classify_max_temp()
@@ -292,21 +323,23 @@ BEGIN
     CASE
        WHEN NEW.max_temp >= 90 THEN
            NEW.max_temp_group := 'Hot';
-       WHEN NEW.max_temp BETWEEN 70 AND 89 THEN
+       WHEN NEW.max_temp >= 70 AND NEW.max_temp < 90 THEN
            NEW.max_temp_group := 'Warm';
-       WHEN NEW.max_temp BETWEEN 50 AND 69 THEN
+       WHEN NEW.max_temp >= 50 AND NEW.max_temp < 70 THEN
            NEW.max_temp_group := 'Pleasant';
-       WHEN NEW.max_temp BETWEEN 33 AND 49 THEN
+       WHEN NEW.max_temp >= 33 AND NEW.max_temp < 50 THEN
-           NEW.max_temp_group :=  'Cold';
+           NEW.max_temp_group := 'Cold';
-       WHEN NEW.max_temp BETWEEN 20 AND 32 THEN
+       WHEN NEW.max_temp >= 20 AND NEW.max_temp < 33 THEN
-           NEW.max_temp_group :=  'Freezing';
+           NEW.max_temp_group := 'Frigid';
-       ELSE NEW.max_temp_group :=  'Inhumane';
+       WHEN NEW.max_temp < 20 THEN
+           NEW.max_temp_group := 'Inhumane';    
+       ELSE NEW.max_temp_group := 'No reading';
     END CASE;
     RETURN NEW;
 END;
 $$ LANGUAGE plpgsql;
 
--- Listing 17-23: Creating the temperature_insert trigger
+-- Listing 17-25: Creating the temperature_insert trigger
 
 CREATE TRIGGER temperature_insert
     BEFORE INSERT
@@ -314,13 +347,14 @@ CREATE TRIGGER temperature_insert
     FOR EACH ROW
     EXECUTE PROCEDURE classify_max_temp();
 
--- Listing 17-24: Inserting rows to test the temperature_update trigger
+-- Listing 17-26: Inserting rows to test the temperature_update trigger
 
-INSERT INTO temperature_test (station_name, observation_date, max_temp, min_temp)
+INSERT INTO temperature_test
 VALUES
-    ('North Station', '1/19/2019', 10, -3),
+    ('North Station', '1/19/2023', 10, -3),
-    ('North Station', '3/20/2019', 28, 19),
+    ('North Station', '3/20/2023', 28, 19),
-    ('North Station', '5/2/2019', 65, 42),
+    ('North Station', '5/2/2023', 65, 42),
-    ('North Station', '8/9/2019', 93, 74);
+    ('North Station', '8/9/2023', 93, 74),
+    ('North Station', '12/14/2023', NULL, NULL);
 
-SELECT * FROM temperature_test;
+SELECT * FROM temperature_test ORDER BY observation_date;

Try_It_Yourself/Try_It_Yourself.sql

@@ -964,7 +964,7 @@ GROUP BY statefp
 ORDER BY square_miles DESC;
 
 -- 2. Using ST_Distance(), determine how many miles separate these two farmers’
--- markets: the Oakleaf Greenmarket (9700 Argyle Forest Blvd, Jacksonville,
+-- markets: The Oakleaf Greenmarket (9700 Argyle Forest Blvd, Jacksonville,
 -- Florida) and Columbia Farmers Market (1701 West Ash Street, Columbia,
 -- Missouri). You’ll need to first find the coordinates for both in the
 -- farmers_markets table.
@@ -1132,8 +1132,89 @@ AS teachers_labs;
 -- When writing a query such as this, it's helpful to work in chunks. Start with the 
 -- outermost query and add the subqueries one by one, testing as you go.
 
-
+----------------------------------------------------------------------------
-
+-- Chapter 17: Saving Time with Views, Functions, and Triggers
-
+----------------------------------------------------------------------------
+
+-- 1. Create a materialized view that displays the number of New York City
+-- taxi trips per hour. Use the taxi data from Chapter 12 and the query in 
+-- Listing 12-8. How do you refresh the view if you need to?
+
+-- Answer:
+
+CREATE MATERIALIZED VIEW nyc_taxi_trips_per_hour AS
+    SELECT
+        date_part('hour', tpep_pickup_datetime) AS trip_hour,
+        count(*)
+    FROM nyc_yellow_taxi_trips
+    GROUP BY trip_hour
+    ORDER BY trip_hour;
+
+SELECT * FROM nyc_taxi_trips_per_hour;
+
+-- To refresh:
+
+REFRESH MATERIALIZED VIEW nyc_taxi_trips_per_hour;
+
+-- 2. In Chapter 11, you learned how to calculate rates per thousand. Turn that
+-- formula into a rate_per_thousand() function that takes three arguments
+-- to calculate the result: observed_number, base_number, and decimal_places.
+
+-- Answer: This uses PL/pgSQL, but you could use a SQL function as well.
+
+CREATE OR REPLACE FUNCTION
+    rate_per_thousand(observed_number numeric,
+                      base_number numeric,
+                      decimal_places integer DEFAULT 1)
+RETURNS numeric(10,2) AS $$
+BEGIN
+    RETURN
+        round(
+        (observed_number / base_number) * 1000, decimal_places
+        );
+END;
+$$ LANGUAGE plpgsql;
+
+-- Test the function:
+
+SELECT rate_per_thousand(50, 11000, 2);
+
+-- 3. In Chapter 10, you worked with the meat_poultry_egg_establishments table that
+-- listed food processing facilities. Write a trigger that automatically adds an 
+-- inspection deadline timestamp six months in the future whenever you insert a new 
+-- facility into the table. Use the inspection_deadline column added in Listing 10-19.
+-- You should be able to describe the steps needed to implement a trigger and how 
+-- the steps relate to each other.
+
+-- Answer:
+-- a) You should have an inspection_deadline column already; if not, add it:
+
+ALTER TABLE meat_poultry_egg_establishments ADD COLUMN inspection_deadline timestamp with time zone;
+
+-- b) Create the function that the trigger will execute.
+
+CREATE OR REPLACE FUNCTION add_inspection_deadline()
+    RETURNS trigger AS $$
+    BEGIN
+       NEW.inspection_deadline = now() + '6 months'::interval; -- Here, we set the inspection date to six months in the future
+    RETURN NEW;
+    END;
+$$ LANGUAGE plpgsql;
+
+-- c) Create the trigger
+
+CREATE TRIGGER inspection_deadline_update
+  BEFORE INSERT
+  ON meat_poultry_egg_establishments
+  FOR EACH ROW
+  EXECUTE PROCEDURE add_inspection_deadline();
+
+-- d) Test the insertion of a company and examine the result
+
+INSERT INTO meat_poultry_egg_establishments(establishment_number, company)
+VALUES ('test123', 'testcompany');
+
+SELECT * FROM meat_poultry_egg_establishments
+WHERE company = 'testcompany';