Learning MySQL By Example
Cover
Introduction
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
1.9. DISTINCT Clause
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. SQL Views
7.1. SQL View Explained
7.2. Benefits of Using Views
7.3. Views That Allow UPDATE Statements
8. SQL Indexes
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
Glossary
Index
3.2

Numeric Functions

ROUND

  • The ROUND function has two parameters. The first is a number, usually a DECIMAL or a FLOAT. The second defines the number of decimals to which the number will be rounded.
  • If no length is provided, the number is rounded to a whole number.

Table 5. ROUND function

Function

Type

Example

Result

ROUND(number[, length])

Number

ROUND(13.37, 1)

13.4

Example:

USE world;
SELECT name, LifeExpectancy, ROUND(LifeExpectancy) 
FROM world.country;

Results:

05_functions.png

FLOOR, CEILING, TRUNCATE

  • FLOOR() will return the next lowest whole number no matter what the decimal point.
  • CEILING() will return the next highest whole number no matter what the decimal point.
  • TRUNCATE() will return the number truncated to the precision specified.

Table 6. FLOOR, CEILING, TRUNCATE functions

Function

Type

Example

Result

FLOOR(number)

number

FLOOR(7.7)

7

CEILING(number)

number

CEILING(6.2)

7

TRUNCATE(NUMBER, length)

number

TRUNCATE(7.9)

7

Example:

USE bike;
SELECT list_price, FLOOR(list_price), CEILING(list_price),
    TRUNCATE(list_price, 0)
FROM product;

Results:

06_functions.png

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CC BY-NC-ND International 4.0: This work is released under a CC BY-NC-ND International 4.0 license, which means that you are free to do with it as you please as long as you (1) properly attribute it, (2) do not use it for commercial gain, and (3) do not create derivative works.

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