Chapter 4 How To Retrieve Data From Multiple Tables PDF

Chapter 4 How to retrieve data from two or more tables Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 1  Objectives Applied  Use the explicit syntax to code an inner join that returns data from a single table or multiple tables.  Us...

Chapter 4 How to retrieve data from two or more tables Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 1  Objectives Applied  Use the explicit syntax to code an inner join that returns data from a single table or multiple tables.  Use the explicit syntax to code an outer join.  Code a union that combines data from a single table or multiple tables. Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 2  Objectives (cont.) Knowledge  Explain when column names need to be qualified.  Describe the proper use of a table alias.  Describe the differences between an inner join, a left outer join, a right outer join, a full outer join, and a cross join.  Describe how to combine inner and outer joins.  Describe the use of the implicit syntax for coding joins.  Describe the use of the USING and NATURAL keywords for coding joins. Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 3  The explicit syntax for an inner join SELECT select_list FROM table_1 [INNER] JOIN table_2 ON join_condition_1 [[INNER] JOIN table_3 ON join_condition_2]... An inner join of the Vendors and Invoices tables SELECT invoice_number, vendor_name FROM vendors INNER JOIN invoices ON vendors.vendor_id = invoices.vendor_id ORDER BY invoice_number (114 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 4  The syntax for an inner join that uses table aliases SELECT select_list FROM table_1 a1 [INNER] JOIN table_2 a2 ON a1.column_name operator a2.column_name [[INNER] JOIN table_3 a3 ON a2.column_name operator a3.column_name]... Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 5  An inner join with aliases for all tables SELECT invoice_number, vendor_name, invoice_due_date, invoice_total - payment_total - credit_total AS balance_due FROM vendors v JOIN invoices i ON v.vendor_id = i.vendor_id WHERE invoice_total - payment_total - credit_total > 0 ORDER BY invoice_due_date DESC Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 6  An inner join with an alias for only one table SELECT invoice_number, line_item_amount, line_item_description FROM invoices JOIN invoice_line_items line_items ON invoices.invoice_id = line_items.invoice_id WHERE account_number = 540 ORDER BY invoice_date (6 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 7  The syntax of a table name that’s qualified with a database name database_name.table_name A join to a table in another database SELECT vendor_name, customer_last_name, customer_first_name, vendor_state AS state, vendor_city AS city FROM vendors v JOIN om.customers c ON v.vendor_zip_code = c.customer_zip ORDER BY state, city (37 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 8  The Customers table (24 rows) The Employees table (9 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 9  An inner join with two conditions SELECT customer_first_name, customer_last_name FROM customers c JOIN employees e ON c.customer_first_name = e.first_name AND c.customer_last_name = e.last_name (1 row) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 10  A self-join that returns vendors from cities in common with other vendors SELECT DISTINCT v1.vendor_name, v1.vendor_city, v1.vendor_state FROM vendors v1 JOIN vendors v2 ON v1.vendor_city = v2.vendor_city AND v1.vendor_state = v2.vendor_state AND v1.vendor_name v2.vendor_name ORDER BY v1.vendor_state, v1.vendor_city (84 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 11  A statement that joins four tables SELECT vendor_name, invoice_number, invoice_date, line_item_amount, account_description FROM vendors v JOIN invoices i ON v.vendor_id = i.vendor_id JOIN invoice_line_items li ON i.invoice_id = li.invoice_id JOIN general_ledger_accounts gl ON li.account_number = gl.account_number WHERE invoice_total - payment_total - credit_total > 0 ORDER BY vendor_name, line_item_amount DESC (11 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 12  The implicit syntax for an inner join SELECT select_list FROM table_1, table_2 [, table_3]... WHERE table_1.column_name operator table_2.column_name [AND table_2.column_name operator table_3.column_name]... Join the Vendors and Invoices tables SELECT invoice_number, vendor_name FROM vendors v, invoices i WHERE v.vendor_id = i.vendor_id ORDER BY invoice_number (114 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 13  Join four tables SELECT vendor_name, invoice_number, invoice_date, line_item_amount, account_description FROM vendors v, invoices i, invoice_line_items li, general_ledger_accounts gl WHERE v.vendor_id = i.vendor_id AND i.invoice_id = li.invoice_id AND li.account_number = gl.account_number AND invoice_total - payment_total - credit_total > 0 ORDER BY vendor_name, line_item_amount DESC (11 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 14  Terms to know  Join  Join condition  Inner join  Ad hoc relationship  Qualified column name  Table alias  Schema  Self-join  Explicit syntax (SQL-92)  Implicit syntax Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 15  The explicit syntax for an outer join SELECT select_list FROM table_1 {LEFT|RIGHT} [OUTER] JOIN table_2 ON join_condition_1 [{LEFT|RIGHT} [OUTER] JOIN table_3 ON join_condition_2]... What outer joins do Joins of this type Retrieve unmatched rows from Left outer join The first (left) table Right outer join The second (right) table Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 16  A left outer join SELECT vendor_name, invoice_number, invoice_total FROM vendors LEFT JOIN invoices ON vendors.vendor_id = invoices.vendor_id ORDER BY vendor_name (202 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 17  The Departments table The Employees table Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 18  The Projects table Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 19  A left outer join SELECT department_name, d.department_number, last_name FROM departments d LEFT JOIN employees e ON d.department_number = e.department_number ORDER BY department_name (8 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 20  A right outer join SELECT department_name, e.department_number, last_name FROM departments d RIGHT JOIN employees e ON d.department_number = e.department_number ORDER BY department_name (9 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 21  Join three tables using left outer joins SELECT department_name, last_name, project_number FROM departments d LEFT JOIN employees e ON d.department_number = e.department_number LEFT JOIN projects p ON e.employee_id = p.employee_id ORDER BY department_name, last_name (8 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 22  Combine an outer and an inner join SELECT department_name, last_name, project_number FROM departments d JOIN employees e ON d.department_number = e.department_number LEFT JOIN projects p ON e.employee_id = p.employee_id ORDER BY department_name, last_name (7 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 23  The syntax for a join that uses the USING keyword SELECT select_list FROM table_1 [{LEFT|RIGHT} [OUTER]] JOIN table_2 USING (join_column_1[, join_column_2]...) [[{LEFT|RIGHT} [OUTER]] JOIN table_3 USING (join_column_1[, join_column_2]...)]... Use the USING keyword to join two tables SELECT invoice_number, vendor_name FROM vendors JOIN invoices USING (vendor_id) ORDER BY invoice_number (114 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 24  Use the USING keyword to join three tables SELECT department_name, last_name, project_number FROM departments JOIN employees USING (department_number) LEFT JOIN projects USING (employee_id) ORDER BY department_name (7 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 25  The syntax for a join that uses the NATURAL keyword SELECT select_list FROM table_1 NATURAL JOIN table_2 [NATURAL JOIN table_3]... Use the NATURAL keyword to join tables SELECT invoice_number, vendor_name FROM vendors NATURAL JOIN invoices ORDER BY invoice_number (114 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 26  Use the NATURAL keyword in a statement that joins three tables SELECT department_name AS dept_name, last_name, project_number FROM departments NATURAL JOIN employees LEFT JOIN projects USING (employee_id) ORDER BY department_name (7 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 27  The explicit syntax for a cross join SELECT select_list FROM table_1 CROSS JOIN table_2 A cross join that uses the explicit syntax SELECT departments.department_number, department_name, employee_id, last_name FROM departments CROSS JOIN employees ORDER BY departments.department_number (45 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 28  The implicit syntax for a cross join SELECT select_list FROM table_1, table_2 A cross join that uses the implicit syntax SELECT departments.department_number, department_name, employee_id, last_name FROM departments, employees ORDER BY departments.department_number (45 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 29  Terms to know  Outer join  Left outer join  Right outer join  Equijoin  Natural join  Cross join  Cartesian product Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 30  The syntax for a union operation SELECT_statement_1 UNION [ALL] SELECT_statement_2 [UNION [ALL] SELECT_statement_3]... [ORDER BY order_by_list] Rules for a union  Each result set must return the same number of columns.  The corresponding columns in each result set must have compatible data types.  The column names in the final result set are taken from the first SELECT clause. Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 31  A union that combines result sets from two different tables SELECT 'Active' AS source, invoice_number, invoice_date, invoice_total FROM active_invoices WHERE invoice_date >= '2014-06-01' UNION SELECT 'Paid' AS source, invoice_number, invoice_date, invoice_total FROM paid_invoices WHERE invoice_date >= '2014-06-01' ORDER BY invoice_total DESC (22 rows) Murach's MySQL, C4 © 2015, Mike Murach & Associates, Inc. Slide 32  A union that combines result sets from a single table SELECT 'Active' AS source, invoice_number, invoice_date, invoice_total FROM invoices WHERE invoice_total - payment_total - credit_total > 0 UNION SELECT 'Paid' AS source, invoice_number, invoice_date, invoice_total FROM invoices WHERE invoice_total - payment_total - credit_total