Learning MySQL By Example

1. How to Retrieve Data From a Single Table

1.1. The Five Clauses of the SELECT Statement

1.2. Column Specifications

1.3. LIKE and REGEXP Operators

1.4. Arithmetic Operators

1.5. Column Aliases

1.6. Comparison Operators

1.7. IS NULL, BETWEEN, IN Operators

1.8. AND, OR, NOT Logical Operators

2. How to Retrieve Data from Multiple Tables

2.1. The JOIN Clause

2.2. Joining More Than Two Tables

2.3. The OUTER JOIN Clause

2.4. How to Code a UNION

3. Using Functions

3.1. Date Functions

3.2. Numeric Functions

3.3. String Functions

4. How to Insert, Update, Delete Data in Tables

4.1. The INSERT Clause With a Column List

4.2. The INSERT Clause Without a Column List

4.4. The UPDATE Clause With a Column List

4.4. The DELETE Clause

5. Summary Queries and Aggregate Functions

5.1. Aggregate Functions

5.2. Grouping Data

5.3. Simple GROUP BY Query

5.4. Improving the GROUP BY Query

5.5. Using the HAVING Clause

5.5. Using the HAVING and WHERE Clauses Together

5.6. COUNT(column_name) and COUNT(*)

5.7. Using the DISTINCT Statement

6. Working With Subqueries

6.1. The Subquery In a SELECT Statement

6.2. The Subquery in an UPDATE statement

6.3. Create a Duplicate Table From An Existing Table

6.4. The Subquery In a Delete Statement

7.1. SQL View Explained

7.2. Benefits of Using Views

7.3. Views That Allow UPDATE Statements

8.1. SQL Indexes Explained

8.2. Clustered vs. Non-clustered Indexes

8.3. Create an Index in Workbench Using an ERD

8.4. How to Manually Add an Index to an Existing Table

1.9

DISTINCT Clause

DISTINCT Keyword

The DISTINCT clause removes duplicate rows from a query.
DISTINCT appears directly after the SELECT clause.
You can specify multiple columns, which means that the combination of columns must be unique.

Table 7. DISTINCT Keyword

Keyword	Description	Order of Evaluation
DISTINCT	Eliminates duplicate rows	1

Example:

SELECT DISTINCT continent, name FROM country ORDER BY continent;

Results:

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