Introduction1. How to Retrieve Data From a Single Table1.1. The Five Clauses of the SELECT Statement1.2. Column Specifications1.3. LIKE and REGEXP Operators1.4. Arithmetic Operators1.5. Column Aliases1.6. Comparison Operators1.7. IS NULL, BETWEEN, IN Operators1.8. AND, OR, NOT Logical Operators1.9. DISTINCT Clause2. How to Retrieve Data from Multiple Tables2.1. The JOIN Clause2.2. Joining More Than Two Tables2.3. The OUTER JOIN Clause2.4. How to Code a UNION3. Using Functions3.1. Date Functions3.2. Numeric Functions3.3. String Functions4. How to Insert, Update, Delete Data in Tables4.1. The INSERT Clause With a Column List4.2. The INSERT Clause Without a Column List4.4. The UPDATE Clause With a Column List4.4. The DELETE Clause5. Summary Queries and Aggregate Functions5.1. Aggregate Functions5.2. Grouping Data5.3. Simple GROUP BY Query5.4. Improving the GROUP BY Query5.5. Using the HAVING Clause5.5. Using the HAVING and WHERE Clauses Together5.6. COUNT(column_name) and COUNT(*)5.7. Using the DISTINCT Statement6. Working With Subqueries6.1. The Subquery In a SELECT Statement6.2. The Subquery in an UPDATE statement6.3. Create a Duplicate Table From An Existing Table 6.4. The Subquery In a Delete Statement7. SQL Views7.1. SQL View Explained7.2. Benefits of Using Views7.3. Views That Allow UPDATE Statements8. SQL Indexes8.1. SQL Indexes Explained8.2. Clustered vs. Non-clustered Indexes8.3. Create an Index in Workbench Using an ERD8.4. How to Manually Add an Index to an Existing TableGlossaryIndex
2.4

How to Code a UNION

How to Code a UNION

  • A UNION combines the results of two or more queries into a single result set
  • Each result set must have the same number of columns
  • The corresponding data types for each column must be compatible. However, the column names may be different from each result set
  • A UNION removes duplicate rows by default
  • You may interfile the results using an ORDERY BY clause if there is a column with a common name.

Code Example:

1 USE world;
2 SELECT name, population
3 FROM city WHERE CountryCode = 'AUS'
4 UNION
5 SELECT name, population
6 FROM country
7 WHERE continent = 'Oceania'
8 ORDER BY name; 

Results:

04_joins.png

SELECT name, population
FROM city
WHERE CountryCode = 'AUS'

UNION

SELECT name, population
FROM country
WHERE continent = 'Oceania'

ORDER BY name;