Let's talk about the problems encountered by PHP when adding, deleting, modifying and checking databases.

PHP is a very popular programming language, especially widely used in Web development. In web applications, dealing with databases is a very common operation. Whether it is adding, deleting, modifying, querying or statistics, you need to use database operation statements. PHP provides some built-in functions to complete these operations, such as mysqli, PDO, etc. However, you still encounter some problems when using these functions. This article will introduce common problems and solutions when adding, deleting, modifying and checking databases in PHP.

1. Add data

It is very common to add data to the database in PHP. You can easily add data by using the INSERT statement. However, you need to pay attention to the following issues:

1. Field type

Before adding data, you need to confirm the data type corresponding to each field in the data table. If the added data type does not match the field type, data insertion will fail. For example, if a field is of integer type but a text type is inserted, the program will report an error.

2. Repeated values

Before inserting data, you need to confirm the unique fields in the data table, such as the primary key. If the inserted data already exists in the table, the insert will fail. For example, if you insert an existing primary key value, the database may return an error message.

3.SQL injection

SQL injection refers to the process in which attackers embed malicious code in SQL statements to achieve illegal operations. For example, in the search function of a certain table, if the keywords entered by the user include the keywords of the SQL statement, the attacker can embed malicious code in it. The workaround is to use prepared statements or escape special characters.

2. Deleting data

Deleting data in the database is also a common operation in PHP. You can use the DELETE statement to complete the deletion of data. However, some problems will also be encountered in practical applications:

1. Deletion conditions

Before deleting data, it is necessary to determine the deletion conditions. If the deletion condition is not set, the data in the entire table will be deleted. Therefore, before writing a DELETE statement, you need to confirm the deletion conditions, such as deleting only data within a certain range or data that meets certain specific conditions.

2. Delete log

When deleting data, you may need to save the deleted data to another table or generate a log. These operations can help developers restore data or record deletions.

3. Update data

Usually the UPDATE statement is used when modifying data. However, you will also encounter some problems when updating data, such as:

1. Update sequence

When executing the UPDATE statement to update data, the order requires special attention. Because if the order of updates is incorrect, data update may fail. For example, if you need to use data from another field in this field when updating data, you need to be very careful in the order of updates.

2. Concurrent update

In the case of high concurrency, multiple users updating the same data at the same time will cause conflicts. The solution is to use optimistic locking or pessimistic locking to ensure the order of data updates.

4. Querying data

It is also very common to query data in applications. Data query can be completed using the SELECT statement in PHP. However, querying data also has the following problems:

1. Response time

When the data in the query data table is very large, the response time may be too long, affecting the user experience. The solution to this problem is to optimize the query statement or use caching technology.

2. Table connection

When executing a related query statement, multiple tables need to be connected to obtain the required data. However, you also need to pay special attention during the process of joining tables, because too many table joins may lead to reduced query efficiency.

3. Data caching

When querying data, you may need to cache the query results to improve query efficiency. Caching can use caching technologies such as Memcache or Redis.

To sum up, there are many problems encountered by PHP when adding, deleting, modifying and checking the database, but there are solutions to these problems. In actual development, appropriate technologies and methods need to be selected according to specific circumstances to improve application performance and user experience.

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