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\n\n4. Run `sudo mkdir -p /etc/paths.d && echo /Applications/Postgres.app/Contents/Versions/latest/bin | sudo tee /etc/paths.d/postgresapp` \n(found [here](https://postgresapp.com/documentation/install.html)) to use `psql` in the terminal. \nClose and open the terminal.\n\n5. Postgres.app will by default create a role and database that matches your current macOS username. You can connect straight away by running `psql`.\n\n6. You should then see something in your terminal that looks like this (with your macOS username in front of the prompt rather than 'postgres'):\n\n\n\n7. You should now be all set up to start using PostgreSQL. For documentation on\ncommand line tools etc see https://postgresapp.com/documentation/\n\n#### Ubuntu\n\nDigital Ocean have got a great article on [getting started with postgres]( https://www.digitalocean.com/community/tutorials/how-to-install-and-use-postgresql-on-ubuntu-16-04). A quick summary is below.\n\n##### Installation\n\n```\nsudo apt-get update\nsudo apt-get install postgresql postgresql-contrib\n```\n\nBy default the only role created is the default 'postgres', so PostgreSQL will only respond to connections from an Ubuntu user called 'postgres'. We need to pretend to be that user and create a role matching our actual Ubuntu username:\n\n```\nsudo -u postgres createuser --interactive\n```\n\nThis command means 'run the command `createuser --interactive` as the user called \"postgres\"'.\n\nWhen asked for the name of the role enter your Ubuntu username. If you're not sure, open a new Terminal tab and run `whoami`.\n\nWhen asked if you want to make the role a superuser, type 'y'.\n\nWe now need to create the database matching the role name, as PostgreSQL expects this. Run:\n\n```\nsudo -u postgres createdb [your user name]\n```\n\nYou can now connect to PostgreSQL by running `psql`.\n\n### Create your first PostgreSQL database\n\n1. To start PostgreSQL, type this command into the terminal: \n`psql` \n\n2. Next type this command into the PostgreSQL interface: \n`CREATE DATABASE test;` \n**NOTE:** Don't forget the semi-colon. If you do, useful error messages won't\nshow up.\n\n3. To check that our database has been created, type `\\l` into the psql prompt.\nYou should see something like this in your terminal:\n\n\n### Create new users for your database\n\n1. If you closed the PostgreSQL server, start it again with: \n` psql` \n\n2. To create a new user, type the following into the psql prompt: \n ```sql\n CREATE USER testuser;\n ```\n\n3. Check that your user has been created. Type `\\du` into the prompt. You should\nsee something like this:\n\nUsers can be given certain permissions to access any given database you have\ncreated.\n\n4. Next we need to give our user permissions to access the test database we\ncreated above. Enter the following command into the `psql` prompt: \n ```sql\n GRANT ALL PRIVILEGES ON DATABASE test TO testuser;\n ```\n\n\n### PostGIS - Spacial and Geographic objects for PostgreSQL\n\n#### PostGIS Installation\nIf you've installed Postgres App as in the example above, you can easily\nextend it to include PostGIS. Follow these steps to begin using PostGIS:\n\n1. Ensure that you're logged in as a user OTHER THAN `postgres`. Follow the\nsteps above to enable your default user to be able to access the `psql` prompt.\n(_[installation step 7](#installation)_)\n\n2. Type the following into the `psql` prompt to add the extension: \n`CREATE EXTENSION postgis;`\n\n#### PostGIS Distance between two sets of coordinates\n\nAfter you've extended PostgreSQL with PostGIS you can begin to use it. Type\nthe following command into the `psql` command line: \n\n```sql\nSELECT ST_Distance(gg1, gg2) As spheroid_dist\nFROM (SELECT\n\tST_GeogFromText('SRID=4326;POINT(-72.1235 42.3521)') As gg1,\n\tST_GeogFromText('SRID=4326;POINT(-72.1235 43.1111)') As gg2\n\t) As foo ;\n```\n\nThis should return `spheroid_dist` along with a value in meters. The\nexample above returns: `84315.42034614` which is rougly 84.3km between the two\npoints.\n\n### Commands\nOnce you are serving the database from your computer\n\n- To change db\n`\\connect database_name;`\n\n- To see the tables in the database\n`\\d;`\n\n- To select (and show in terminal) all tables\n`SELECT * FROM table_name`\n\n\n- To make a table\n`CREATE TABLE table_name (col_name1, col_name2)`\n\n- To add a row\n`INSERT INTO table_name ( col_name )\nVALUES ( col_value)`\ncol_name only require if only some of the cols are being filled out\n\n- To edit a column to a table \n`ALTER TABLE table_name\n ALTER COLUMN column_name SET DEFAULT expression`\n\n- To add a column to a table \n`ALTER TABLE table_name\n ADD COLUMN column_name data_type`\n\n- To find the number of instances where the word “Day” is present in the title of a table\n`SELECT count(title) FROM table_name WHERE title LIKE '%Day%’;`\n\n- To delete a row in a table\n`DELETE FROM table_name\n WHERE column_name = ‘hello';`\n\n\nPostgresql follows the SQL convention of calling relations TABLES, attributes COLUMNs and tuples ROWS\n\n**Transaction**\nAll or nothing, if something fails the other commands are rolled back like nothing happened\n\n**Reference**\nWhen a table is being created you can reference a column in another table to make sure any value which is added to that column exists in the referenced table.\n\n```sql\nCREATE TABLE cities (\n name text NOT NULL,\n postal_code varchar(9) CHECK (postal_code <> ''),\n country_code char(2) REFERENCES countries,\n PRIMARY KEY (country_code, postal_code)\n);\n```\n\n`<>` means not equal\n\n\n**Join reads**\nYou can join tables together when reading them,\n\n**Inner Join**\nJoins together two tables by specifying a column in each to join them by i.e.\n\n```sql\nSELECT cities.*, country_name\n FROM cities INNER JOIN countries\n ON cities.country_code = countries.country_code;\n```\n\nThis will select all of the columns in both the countries\nand cities tables the data, the rows are matched up by `country_code`.\n\n**Grouping**\nYou can put rows into groups where the group is defined by a shared value in a particular column.\n\n```sql\nSELECT venue_id, count(*)\n FROM events\n GROUP BY venue_id;\n```\n\nThis will group the rows together by the venue_id,\ncount is then performed on each of the groups.\n\n### Learning Resources\n\n+ Node-hero: https://blog.risingstack.com/node-js-database-tutorial\n+ Pluralsight postgres getting started:\n https://www.pluralsight.com/courses/postgresql-getting-started\n+ Tech Republic Postgres setup:\n https://www.techrepublic.com/article/diy-a-postgresql-database-server-setup-anyone-can-handle/\n+ PostGIS installation: https://postgis.net/install\n+ PostGIS docs: https://postgis.net/docs/manual-2.3\n+ SQl Tutorials: https://www.scaler.com/topics/sql/\n+ PostGIS ST_Distance: https://postgis.net/docs/ST_Distance.html\n+ Foreign Key Constraints:\n + https://en.wikipedia.org/wiki/Foreign_key\n + https://www.postgresqltutorial.com/postgresql-tutorial/postgresql-foreign-key/\n + https://tableplus.io/blog/2018/08/postgresql-how-to-add-a-foreign-key.html\n+ Graphical Interface (GUI) tools:\nhttps://wiki.postgresql.org/wiki/Community_Guide_to_PostgreSQL_GUI_Tools\n"
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