Chapter 17 updates
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@ -22,6 +22,7 @@ CREATE OR REPLACE VIEW nevada_counties_pop_2019 AS
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SELECT *
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FROM nevada_counties_pop_2019
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ORDER BY county_fips
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LIMIT 5;
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-- Listing 17-3: Creating a view showing population change for US counties
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@ -33,7 +34,6 @@ CREATE OR REPLACE VIEW county_pop_change_2019_2010 AS
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c2019.county_fips,
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c2019.pop_est_2019 AS pop_2019,
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c2010.estimates_base_2010 AS pop_2010,
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c2019.pop_est_2019 - c2010.estimates_base_2010 AS raw_change,
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round( (c2019.pop_est_2019::numeric - c2010.estimates_base_2010)
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/ c2010.estimates_base_2010 * 100, 1 ) AS pct_change_2019_2010
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FROM us_counties_pop_est_2019 AS c2019
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@ -42,7 +42,7 @@ CREATE OR REPLACE VIEW county_pop_change_2019_2010 AS
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AND c2019.county_fips = c2010.county_fips
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ORDER BY c2019.state_fips, c2019.county_fips;
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-- Listing 17-4: Selecting columns from the county_pop_change_2010_2000 view
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-- Listing 17-4: Selecting columns from the county_pop_change_2019_2010 view
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SELECT county_name,
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state_name,
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@ -50,9 +50,32 @@ SELECT county_name,
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pct_change_2019_2010
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FROM county_pop_change_2019_2010
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WHERE state_name = 'Nevada'
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ORDER BY county_fips
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LIMIT 5;
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-- Listing 17-5: Creating a view on the employees table
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-- Listing 17-5: Creating a materialized view
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DROP VIEW nevada_counties_pop_2019;
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CREATE MATERIALIZED VIEW nevada_counties_pop_2019 AS
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SELECT county_name,
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state_fips,
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county_fips,
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pop_est_2019
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FROM us_counties_pop_est_2019
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WHERE state_name = 'Nevada'
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ORDER BY county_fips;
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-- Listing 17-6: Refreshing a materialized view
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REFRESH MATERIALIZED VIEW nevada_counties_pop_2019;
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-- Bonus: You can drop a materialized view using:
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-- DROP MATERIALIZED VIEW nevada_counties_pop_2019;
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SELECT * FROM employees ORDER BY emp_id;
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-- Listing 17-7: Creating a view on the employees table
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CREATE OR REPLACE VIEW employees_tax_dept AS
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SELECT emp_id,
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@ -64,9 +87,9 @@ CREATE OR REPLACE VIEW employees_tax_dept AS
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ORDER BY emp_id
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WITH LOCAL CHECK OPTION;
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SELECT * FROM employees_tax_dept;
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-- SELECT * FROM employees;
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-- Listing 17-6: Successful and rejected inserts via the employees_tax_dept view
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SELECT * FROM employees_tax_dept ORDER BY emp_id;
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-- Listing 17-8: Successful and rejected inserts via the employees_tax_dept view
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INSERT INTO employees_tax_dept (emp_id, first_name, last_name, dept_id)
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VALUES (5, 'Suzanne', 'Legere', 1);
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@ -74,34 +97,35 @@ VALUES (5, 'Suzanne', 'Legere', 1);
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INSERT INTO employees_tax_dept (emp_id, first_name, last_name, dept_id)
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VALUES (6, 'Jamil', 'White', 2);
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-- optional:
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SELECT * FROM employees_tax_dept;
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SELECT * FROM employees_tax_dept ORDER BY emp_id;
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SELECT * FROM employees;
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SELECT * FROM employees ORDER BY emp_id;
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-- Listing 17-7: Updating a row via the employees_tax_dept view
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-- Listing 17-9: Updating a row via the employees_tax_dept view
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UPDATE employees_tax_dept
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SET last_name = 'Le Gere'
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WHERE emp_id = 5;
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SELECT * FROM employees_tax_dept;
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SELECT * FROM employees_tax_dept ORDER BY emp_id;
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-- Bonus: This will fail because the salary column is not in the view
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UPDATE employees_tax_dept
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SET salary = 100000
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WHERE emp_id = 5;
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-- Listing 17-8: Deleting a row via the employees_tax_dept view
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-- Listing 17-10: Deleting a row via the employees_tax_dept view
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DELETE FROM employees_tax_dept
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WHERE emp_id = 5;
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-- FUNCTIONS
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-- https://www.postgresql.org/docs/current/static/plpgsql.html
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-- FUNCTIONS AND PROCEDURES
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-- https://www.postgresql.org/docs/current/sql-createfunction.html
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-- https://www.postgresql.org/docs/current/sql-createprocedure.html
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-- https://www.postgresql.org/docs/current/plpgsql.html
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-- Listing 17-9: Creating a percent_change function
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-- Listing 17-11: Creating a percent_change function
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-- To delete this function: DROP FUNCTION percent_change(numeric,numeric,integer);
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CREATE OR REPLACE FUNCTION
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@ -109,23 +133,26 @@ percent_change(new_value numeric,
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old_value numeric,
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decimal_places integer DEFAULT 1)
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RETURNS numeric AS
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'SELECT round(
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((new_value - old_value) / old_value) * 100, decimal_places
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);'
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$$
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SELECT round(
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((new_value - old_value) / old_value) * 100, decimal_places
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);
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$$
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LANGUAGE SQL
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IMMUTABLE
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RETURNS NULL ON NULL INPUT;
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-- Listing 17-10: Testing the percent_change() function
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-- Listing 17-12: Testing the percent_change() function
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SELECT percent_change(110, 108, 2);
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-- Listing 17-11: Testing percent_change() on Census data
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-- Listing 17-13: Testing percent_change() on Census data
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SELECT c2019.county_name,
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c2019.state_name,
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c2019.pop_est_2019 AS pop_2019,
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percent_change(c2019.pop_est_2019, c2010.estimates_base_2010) AS pct_chg_func,
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percent_change(c2019.pop_est_2019,
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c2010.estimates_base_2010) AS pct_chg_func,
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round( (c2019.pop_est_2019::numeric - c2010.estimates_base_2010)
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/ c2010.estimates_base_2010 * 100, 1 ) AS pct_chg_formula
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FROM us_counties_pop_est_2019 AS c2019
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@ -135,7 +162,7 @@ ON c2019.state_fips = c2010.state_fips
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ORDER BY pct_chg_func DESC
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LIMIT 5;
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-- Listing 17-12: Adding a column to the teachers table and seeing the data
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-- Listing 17-14: Adding a column to the teachers table and seeing the data
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ALTER TABLE teachers ADD COLUMN personal_days integer;
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@ -144,52 +171,56 @@ SELECT first_name,
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hire_date,
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personal_days
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FROM teachers;
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SELECT * FROM teachers;
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-- Listing 17-13: Creating an update_personal_days() function
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CREATE OR REPLACE FUNCTION update_personal_days()
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RETURNS void AS $$
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-- Listing 17-15: Creating an update_personal_days() procedure
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CREATE OR REPLACE PROCEDURE update_personal_days()
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LANGUAGE plpgsql
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AS $$
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BEGIN
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UPDATE teachers
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SET personal_days =
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CASE WHEN (now() - hire_date) BETWEEN '5 years'::interval
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AND '10 years'::interval THEN 4
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WHEN (now() - hire_date) > '10 years'::interval THEN 5
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CASE WHEN (now() - hire_date) >= '10 years'::interval
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AND (now() - hire_date) < '15 years'::interval THEN 4
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WHEN (now() - hire_date) >= '15 years'::interval
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AND (now() - hire_date) < '20 years'::interval THEN 5
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WHEN (now() - hire_date) >= '20 years'::interval
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AND (now() - hire_date) < '25 years'::interval THEN 6
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WHEN (now() - hire_date) >= '25 years'::interval THEN 7
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ELSE 3
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END;
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RAISE NOTICE 'personal_days updated!';
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END;
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$$ LANGUAGE plpgsql;
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END
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$$;
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-- To run the function:
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SELECT update_personal_days();
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-- To invoke the procedure:
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CALL update_personal_days();
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-- Listing 17-14: Enabling the PL/Python procedural language
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-- Listing 17-16: Enabling the PL/Python procedural language
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CREATE EXTENSION plpythonu; -- doesn't work on macOS with PostgresApp
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CREATE EXTENSION plpython3u; -- doesn't work on macOS with PostgresApp
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CREATE EXTENSION plpython3u;
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-- Listing 17-15: Using PL/Python to create the trim_county() function
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-- Listing 17-17: Using PL/Python to create the trim_county() function
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CREATE OR REPLACE FUNCTION trim_county(input_string text)
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RETURNS text AS $$
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import re
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cleaned = re.sub(r' County', '', input_string)
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return cleaned
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$$ LANGUAGE plpythonu;
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$$ LANGUAGE plpython3u;
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-- Listing 17-16: Testing the trim_county() function
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-- Listing 17-18: Testing the trim_county() function
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SELECT geo_name,
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trim_county(geo_name)
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FROM us_counties_2010
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SELECT county_name,
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trim_county(county_name)
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FROM us_counties_pop_est_2019
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ORDER BY state_fips, county_fips
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LIMIT 5;
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-- TRIGGERS
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-- Listing 17-17: Creating the grades and grades_history tables
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-- Listing 17-19: Creating the grades and grades_history tables
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CREATE TABLE grades (
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student_id bigint,
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@ -216,7 +247,7 @@ CREATE TABLE grades_history (
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PRIMARY KEY (student_id, course_id, change_time)
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);
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-- Listing 17-18: Creating the record_if_grade_changed() function
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-- Listing 17-20: Creating the record_if_grade_changed() function
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CREATE OR REPLACE FUNCTION record_if_grade_changed()
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RETURNS trigger AS
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@ -242,7 +273,7 @@ BEGIN
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END;
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$$ LANGUAGE plpgsql;
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-- Listing 17-19: Creating the grades_update trigger
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-- Listing 17-21: Creating the grades_update trigger
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CREATE TRIGGER grades_update
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AFTER UPDATE
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@ -250,13 +281,13 @@ CREATE TRIGGER grades_update
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FOR EACH ROW
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EXECUTE PROCEDURE record_if_grade_changed();
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-- Listing 17-20: Testing the grades_update trigger
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-- Listing 17-22: Testing the grades_update trigger
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-- Initially, there should be 0 records in the history
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SELECT * FROM grades_history;
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-- Check the grades
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SELECT * FROM grades;
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SELECT * FROM grades ORDER BY student_id, course_id;
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-- Update a grade
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UPDATE grades
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@ -271,7 +302,7 @@ SELECT student_id,
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new_grade
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FROM grades_history;
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-- Listing 17-21: Creating a temperature_test table
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-- Listing 17-23: Creating a temperature_test table
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CREATE TABLE temperature_test (
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station_name text,
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@ -282,7 +313,7 @@ CREATE TABLE temperature_test (
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PRIMARY KEY (station_name, observation_date)
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);
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-- Listing 17-22: Creating the classify_max_temp() function
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-- Listing 17-24: Creating the classify_max_temp() function
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-- CHECK AGAINST CATEGORIES USED PREVIOUSLY
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CREATE OR REPLACE FUNCTION classify_max_temp()
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@ -292,21 +323,23 @@ BEGIN
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CASE
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WHEN NEW.max_temp >= 90 THEN
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NEW.max_temp_group := 'Hot';
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WHEN NEW.max_temp BETWEEN 70 AND 89 THEN
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WHEN NEW.max_temp >= 70 AND NEW.max_temp < 90 THEN
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NEW.max_temp_group := 'Warm';
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WHEN NEW.max_temp BETWEEN 50 AND 69 THEN
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WHEN NEW.max_temp >= 50 AND NEW.max_temp < 70 THEN
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NEW.max_temp_group := 'Pleasant';
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WHEN NEW.max_temp BETWEEN 33 AND 49 THEN
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NEW.max_temp_group := 'Cold';
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WHEN NEW.max_temp BETWEEN 20 AND 32 THEN
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NEW.max_temp_group := 'Freezing';
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ELSE NEW.max_temp_group := 'Inhumane';
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WHEN NEW.max_temp >= 33 AND NEW.max_temp < 50 THEN
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NEW.max_temp_group := 'Cold';
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WHEN NEW.max_temp >= 20 AND NEW.max_temp < 33 THEN
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NEW.max_temp_group := 'Frigid';
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WHEN NEW.max_temp < 20 THEN
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NEW.max_temp_group := 'Inhumane';
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ELSE NEW.max_temp_group := 'No reading';
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END CASE;
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RETURN NEW;
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END;
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$$ LANGUAGE plpgsql;
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-- Listing 17-23: Creating the temperature_insert trigger
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-- Listing 17-25: Creating the temperature_insert trigger
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CREATE TRIGGER temperature_insert
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BEFORE INSERT
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@ -314,13 +347,14 @@ CREATE TRIGGER temperature_insert
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FOR EACH ROW
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EXECUTE PROCEDURE classify_max_temp();
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-- Listing 17-24: Inserting rows to test the temperature_update trigger
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-- Listing 17-26: Inserting rows to test the temperature_update trigger
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INSERT INTO temperature_test (station_name, observation_date, max_temp, min_temp)
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INSERT INTO temperature_test
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VALUES
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('North Station', '1/19/2019', 10, -3),
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('North Station', '3/20/2019', 28, 19),
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('North Station', '5/2/2019', 65, 42),
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('North Station', '8/9/2019', 93, 74);
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('North Station', '1/19/2023', 10, -3),
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('North Station', '3/20/2023', 28, 19),
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('North Station', '5/2/2023', 65, 42),
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('North Station', '8/9/2023', 93, 74),
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('North Station', '12/14/2023', NULL, NULL);
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SELECT * FROM temperature_test;
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SELECT * FROM temperature_test ORDER BY observation_date;
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@ -964,7 +964,7 @@ GROUP BY statefp
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ORDER BY square_miles DESC;
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-- 2. Using ST_Distance(), determine how many miles separate these two farmers’
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-- markets: the Oakleaf Greenmarket (9700 Argyle Forest Blvd, Jacksonville,
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-- markets: The Oakleaf Greenmarket (9700 Argyle Forest Blvd, Jacksonville,
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-- Florida) and Columbia Farmers Market (1701 West Ash Street, Columbia,
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-- Missouri). You’ll need to first find the coordinates for both in the
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-- farmers_markets table.
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@ -1132,8 +1132,89 @@ AS teachers_labs;
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-- When writing a query such as this, it's helpful to work in chunks. Start with the
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-- outermost query and add the subqueries one by one, testing as you go.
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----------------------------------------------------------------------------
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-- Chapter 17: Saving Time with Views, Functions, and Triggers
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----------------------------------------------------------------------------
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-- 1. Create a materialized view that displays the number of New York City
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-- taxi trips per hour. Use the taxi data from Chapter 12 and the query in
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-- Listing 12-8. How do you refresh the view if you need to?
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-- Answer:
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CREATE MATERIALIZED VIEW nyc_taxi_trips_per_hour AS
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SELECT
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date_part('hour', tpep_pickup_datetime) AS trip_hour,
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count(*)
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FROM nyc_yellow_taxi_trips
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GROUP BY trip_hour
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ORDER BY trip_hour;
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SELECT * FROM nyc_taxi_trips_per_hour;
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-- To refresh:
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REFRESH MATERIALIZED VIEW nyc_taxi_trips_per_hour;
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-- 2. In Chapter 11, you learned how to calculate rates per thousand. Turn that
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-- formula into a rate_per_thousand() function that takes three arguments
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-- to calculate the result: observed_number, base_number, and decimal_places.
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-- Answer: This uses PL/pgSQL, but you could use a SQL function as well.
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CREATE OR REPLACE FUNCTION
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rate_per_thousand(observed_number numeric,
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base_number numeric,
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decimal_places integer DEFAULT 1)
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RETURNS numeric(10,2) AS $$
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BEGIN
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RETURN
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round(
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(observed_number / base_number) * 1000, decimal_places
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);
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END;
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$$ LANGUAGE plpgsql;
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-- Test the function:
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SELECT rate_per_thousand(50, 11000, 2);
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-- 3. In Chapter 10, you worked with the meat_poultry_egg_establishments table that
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-- listed food processing facilities. Write a trigger that automatically adds an
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-- inspection deadline timestamp six months in the future whenever you insert a new
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-- facility into the table. Use the inspection_deadline column added in Listing 10-19.
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-- You should be able to describe the steps needed to implement a trigger and how
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-- the steps relate to each other.
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-- Answer:
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-- a) You should have an inspection_deadline column already; if not, add it:
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ALTER TABLE meat_poultry_egg_establishments ADD COLUMN inspection_deadline timestamp with time zone;
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-- b) Create the function that the trigger will execute.
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CREATE OR REPLACE FUNCTION add_inspection_deadline()
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RETURNS trigger AS $$
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BEGIN
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NEW.inspection_deadline = now() + '6 months'::interval; -- Here, we set the inspection date to six months in the future
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RETURN NEW;
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END;
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$$ LANGUAGE plpgsql;
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-- c) Create the trigger
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CREATE TRIGGER inspection_deadline_update
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BEFORE INSERT
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ON meat_poultry_egg_establishments
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FOR EACH ROW
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EXECUTE PROCEDURE add_inspection_deadline();
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-- d) Test the insertion of a company and examine the result
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INSERT INTO meat_poultry_egg_establishments(establishment_number, company)
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VALUES ('test123', 'testcompany');
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SELECT * FROM meat_poultry_egg_establishments
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WHERE company = 'testcompany';
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