How to operate php database query 10 statements

PHP is a programming language widely used in web development. As web developers, we often need to query data in the database. In this article, I will introduce 10 PHP query statements that allow you to query the database easily.

1. Query a single field

When you need to query a single field of a table, you can use the following statement:

SELECT field_name FROM table_name

For example, if we need to query the "username" field in a table named "users", we can use the following code:

$query = "SELECT username FROM users";
$result = mysqli_query($connection, $query);

2. Query multiple fields

When you need to query multiple fields of a table, you can use the following statement:

SELECT field1, field2, field3 FROM table_name

For example, if we need to query the fields in a table named "users" For the "username", "email" and "phone" fields, you can use the following code:

$query = "SELECT username, email, phone FROM users";
$result = mysqli_query($connection, $query);

3. Query all fields

When you need to query To query all fields in a table, you can use the following statement:

SELECT * FROM table_name

For example, if we need to query all fields in a table named "users", we can use the following code:

$query = "SELECT * FROM users";
$result = mysqli_query($connection, $query);

4. Conditional query

When you need to query data that meets certain conditions, you can use the following statement:

SELECT field1, field2 FROM table_name WHERE condition

For example, If we need to query the "username" and "email" fields in a table named "users", where "age" is less than 30 years old, we can use the following code:

$query = "SELECT username, email FROM users WHERE age < 30";
$result = mysqli_query($connection, $query);

5. Sort Query

When you need to sort data according to certain rules, you can use the following statement:

SELECT field1, field2 FROM table_name ORDER BY field1 ASC

For example, if we need to query a file named "username" and "email" fields in the "users" table, and sort by the "username" field in ascending order, you can use the following code:

$query = "SELECT username, email FROM users ORDER BY username ASC";
$result = mysqli_query($connection, $query);

6. Group query

When you need to perform group statistics based on a certain field, you can use the following statement:

SELECT field1, COUNT(field2) FROM table_name GROUP BY field1

For example, if we need to query " country" field, and count the number of users in each country, you can use the following code:

$query = "SELECT country, COUNT(id) FROM users GROUP BY country";
$result = mysqli_query($connection, $query);

7. Join query

When you need to query When querying data in two or more tables, you can use the following statement:

SELECT field1, field2 FROM table1 INNER JOIN table2 ON table1.field = table2.field

For example, if we need to query "username", "country" and "cities" in a table named "users" "City" field in the table and join based on the "city_id" of "users" and the "id" of "cities", you can use the following code:

$query = "SELECT username, country, city FROM users INNER JOIN cities ON users.city_id = cities.id";
$result = mysqli_query($connection, $query);

8. Insert data

When you need to insert data into the database, you can use the following statement:

INSERT INTO table_name (field1, field2, field3) VALUES ('value1', 'value2', 'value3')

For example, if we need to insert into a table named "users" For a new piece of data, you can use the following code:

$query = "INSERT INTO users (username, email, password) VALUES ('John Doe', 'johndoe@example.com', '123456')";
mysqli_query($connection, $query);

9. Update data

When you need to update the data in the database, you can use the following statement :

UPDATE table_name SET field1 = 'value1', field2 = 'value2' WHERE condition

For example, if we need to modify all the "email" fields in a table named "users" to "newemail@example.com", and "username" is "John Doe", you can use the following code:

$query = "UPDATE users SET email = 'newemail@example.com' WHERE username = 'John Doe'";
mysqli_query($connection, $query);

10. Delete data

When you need to delete data in the database, you can use the following Statement:

DELETE FROM table_name WHERE condition

For example, if we need to delete all records in a table named "users" whose "username" field is "John Doe", we can use the following code:

$query = "DELETE FROM users WHERE username = 'John Doe'";
mysqli_query($connection, $query);

The above are 10 PHP query statements. These statements can help us easily query and operate data in the database. Of course, in actual applications, it needs to be adjusted and optimized according to specific business needs.

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