How to query empty fields with MySQL

MySQL is an open source relational database management system that is widely used in various web applications and data-driven websites. In daily database development work, we often need to query and analyze data. Among them, querying whether a field is empty is a very common operation. This article will introduce how to use MySQL to query empty fields and provide readers with practical database query skills.

1. Basic concepts

In MySQL, an empty field usually means that the field has not been assigned a value or is assigned a value of NULL. In actual database application scenarios, unassigned fields may have multiple reasons. For example, some fields in some tables may themselves be empty, or the user may have forgotten to fill in the field when entering data.

For such unassigned fields, we need to query for further processing of data. Below are some basic MySQL query statements.

2. Basic syntax for querying empty fields

In MySQL, we can use IS NULL or IS NOT NULL to query whether a field is empty. The following is a simple example:

SELECT * FROM table_name WHERE column_name IS NULL;

This statement means to query all records in the table_name table where the field column_name is empty. Similarly, if we want to find non-empty fields, we can use the following statement:

SELECT * FROM table_name WHERE column_name IS NOT NULL;

The meaning of this statement is to query all records in the table_name table where the field column_name is not empty.

3. Example Demonstration

Below, we use an example to demonstrate how to use MySQL to query empty fields. Suppose we have a student information table, which contains basic information such as the student's name, age, gender, etc. Now, we want to query the students whose gender field is not filled in.

First, we can use the following statement to query student records that do not fill in the gender field:

SELECT * FROM students WHERE gender IS NULL;

This statement will return all records in the students table where the field gender is empty. As shown in the figure below:

#We can also query non-empty fields. Suppose we want to query student records that have filled in the gender field, we can use the following statement:

SELECT * FROM students WHERE gender IS NOT NULL;

This statement will return all records in the students table where the field gender is not empty. As shown in the figure below:

4. Summary

This article introduces how to use MySQL to query empty fields. In actual database applications, this type of operation is very common. By using the IS NULL and IS NOT NULL statements, we can quickly filter the required records. When writing MySQL query statements, you need to be aware that different data types may affect the way null fields are handled. At the same time, in actual applications, in order to ensure the accuracy of data, we also need to effectively process and fill empty fields.

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