Create query.sql

Author: elmoallistair

Introduction to Relational Databases in SQL/01 Your first database/02 Query information_schema with SELECT/query.sql

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+-- Query the right table in information_schema
+SELECT table_name
+FROM information_schema.tables
+-- Specify the correct table_schema value
+WHERE table_schema = 'public';
+
+-- Query the right table in information_schema to get columns
+SELECT column_name, data_type
+FROM information_schema.columns
+WHERE table_name = 'university_professors' AND table_schema = 'public';
+
+-- Query the first five rows of our table
+SELECT *
+FROM university_professors
+LIMIT 5;

Introduction to Relational Databases in SQL/01 Your first database/03 CREATE your first few TABLEs/query.sql

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+-- Create a table for the professors entity type
+CREATE TABLE professors (
+ firstname text,
+ lastname text
+);
+
+-- Print the contents of this table
+SELECT *
+FROM professors
+
+-- Create a table for the universities entity type
+CREATE TABLE universities (
+ university_shortname text,
+ university text,
+ university_city text
+);
+
+-- Print the contents of this table
+SELECT *
+FROM universities

Introduction to Relational Databases in SQL/01 Your first database/04 ADD a COLUMN with ALTER TABLE/query.sql

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+-- Add the university_shortname column
+ALTER TABLE professors
+ADD COLUMN university_shortname text;
+
+-- Print the contents of this table
+SELECT *
+FROM professors

Introduction to Relational Databases in SQL/01 Your first database/05 RENAME and DROP COLUMNs in affiliations/query.sql

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+-- Rename the organisation column
+ALTER TABLE affiliations
+RENAME COLUMN organisation TO organization;
+
+-- Delete the university_shortname column
+ALTER TABLE affiliations
+DROP COLUMN university_shortname;

Introduction to Relational Databases in SQL/01 Your first database/06 Migrate data with INSERT INTO SELECT DISTINCT/query.sql

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+-- Insert unique professors into the new table
+INSERT INTO professors
+SELECT DISTINCT firstname, lastname, university_shortname
+FROM university_professors;
+
+-- Doublecheck the contents of professors
+SELECT *
+FROM professors;
+
+-- Insert unique affiliations into the new table
+INSERT INTO affiliations
+SELECT DISTINCT firstname, lastname, function, organization
+FROM university_professors;
+
+-- Doublecheck the contents of affiliations
+SELECT *
+FROM affiliations;

Introduction to Relational Databases in SQL/01 Your first database/07 Delete tables with DROP TABLE/query.sql

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+-- Delete the university_professors table
+DROP TABLE university_professors;

Introduction to Relational Databases in SQL/02 Enforce data consistency with attribute constraints/01 Types of database constraints/readme.md

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+## Types of database constraints
+
+Which of the following is not used to enforce a database constraint?
+
+**Possible Answers**
+
+* Foreign keys
+* SQL aggregate functions
+* The BIGINT data type
+* Primary keys
+
+**Answer**
+
+> SQL aggregate functions

Introduction to Relational Databases in SQL/02 Enforce data consistency with attribute constraints/02 Conforming with data types/query.sql

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+-- Let's add a record to the table
+INSERT INTO transactions (transaction_date, amount, fee)
+VALUES ('2018-09-24', 5454, '30');
+
+-- Doublecheck the contents
+SELECT *
+FROM transactions;

Introduction to Relational Databases in SQL/02 Enforce data consistency with attribute constraints/04 Change types with ALTER COLUMN/query.sql

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+-- Select the university_shortname column
+SELECT DISTINCT(university_shortname)
+FROM professors;
+
+-- Specify the correct fixed-length character type
+ALTER TABLE professors
+ALTER COLUMN university_shortname
+TYPE char(3);
+
+-- Change the type of firstname
+ALTER TABLE professors
+ALTER COLUMN firstname
+TYPE varchar(64);

Introduction to Relational Databases in SQL/02 Enforce data consistency with attribute constraints/05 Convert types USING a function/query.sql

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+-- Convert the values in firstname to a max. of 16 characters
+ALTER TABLE professors
+ALTER COLUMN firstname
+TYPE varchar(16)
+USING SUBSTRING(firstname FROM 1 FOR 16)