MySQL Comparison Query Techniques: A Comprehensive Guide（mysql比较查询）

MySQL Comparison Query Techniques: A Comprehensive Guide

MySQL is one of the most widely used open-source database management systems in the world. As such, it is important to master its comparison query techniques. Comparison queries are used to compare data stored in different tables or columns. In this comprehensive guide, we will explore various comparison query techniques in MySQL.

1. Equality Comparison

The most basic and widely used technique is equality comparison. It simply compares two values to determine if they are equal. For example:

SELECT * FROM persons WHERE age = 30;

This query will return all rows where age is equal to 30.

2. Inequality Comparison

Another commonly used technique is inequality comparison. It compares two values to determine whether they are not equal. For example:

SELECT * FROM persons WHERE age != 30;

This query will return all rows where age is not equal to 30.

3. Greater Than Comparison

This technique compares two values to determine whether the left value is greater than the right value. For example:

SELECT * FROM persons WHERE age > 30;

This query will return all rows where age is greater than 30.

4. Less Than Comparison

This technique compares two values to determine whether the left value is less than the right value. For example:

SELECT * FROM persons WHERE age

This query will return all rows where age is less than 30.

5. Greater Than or Equal To Comparison

This technique compares two values to determine whether the left value is greater than or equal to the right value. For example:

SELECT * FROM persons WHERE age >= 30;

This query will return all rows where age is greater than or equal to 30.

6. Less Than or Equal To Comparison

This technique compares two values to determine whether the left value is less than or equal to the right value. For example:

SELECT * FROM persons WHERE age

This query will return all rows where age is less than or equal to 30.

7. Null Comparison

Null values are values that have not been assigned a value. The null comparison technique is used to compare fields that may or may not contain null values. For example:

SELECT * FROM persons WHERE age IS NULL;

This query will return all rows where age has a null value.

8. Not Null Comparison

Not null comparison technique is used to compare fields that do not contain null values. For example:

SELECT * FROM persons WHERE age IS NOT NULL;

This query will return all rows where age does not have null value.

9. Like Comparison

Like comparison technique is used to compare fields based on the pattern matching. For example:

SELECT * FROM persons WHERE name like “smith%”;

This query will return all rows where the name starts with “smith”.

In conclusion, these are some of the most commonly used comparison query techniques in MySQL. By mastering these techniques, you will be able to manipulate data and extract useful information from databases. It is important to make sure that you have a good understanding of each technique to make the most out of them.