PHP Warning: mysqli_query(): Solution to Empty query

When using PHP to develop web applications, you often encounter various problems. Among them, some common problems are related to MySQL database. One problem is the "PHP Warning: mysqli_query(): Empty query" error. This article explains the causes of this error and how to fix it.

First, let’s see what this error means. When you execute a MySQL query using the mysqli_query function, this error occurs if the query is empty. This means that you tried to execute a MySQL query, but the query string was empty. For example, the query string in the following code is empty:

$result = mysqli_query($conn, "");

This error will occur when you try to execute this query. This can happen in a variety of situations. Here are some of the reasons:

1. Syntax error: A syntax error in the query string may cause it to be empty. For example, if you accidentally leave a parenthesis or quotation mark, it may cause the query string to be empty.
2. Variables are not defined: If you use PHP variables in the query string, and these variables are not defined before the query, it may cause the query string to be empty.
3. Database connection error: If there is a bug in your code and it fails to connect to the MySQL database correctly, the query may be empty.

So, how to solve this problem? Here are some possible solutions:

1. Find syntax errors in the query string: You should print the query string with an echo statement so that you can check it for syntax errors. When looking for syntax errors, carefully check parentheses, quotation marks, and commas.

For example, the following query string:

$sql = "SELECT * FROM myTable WHERE id = ";

When the $id variable is not defined, the query The string is empty. You should add a $id value, or change the query string to:

$sql = "SELECT * FROM myTable";

2. Check if the MySQL connection is OK: If you can't Correctly connected to the MySQL database, the query may be empty. You can make sure that the MySQL server is running and that the username and password are correct, and you can also try changing the port number of the MySQL server.
3. Use the mysqli_real_escape_string function to escape the query string: If you are building a query string and using variables, it is recommended to use the mysqli_real_escape_string function to escape these variables. This will ensure that your query string does not contain incorrect characters, thus preventing the query string from being empty.

For example, the following code uses variables to build a query string:

$name = "Tom";
$sql = "SELECT * FROM myTable WHERE name = '$name '";

You can use the mysqli_real_escape_string function to escape variables:

$name = "Tom";
$name = mysqli_real_escape_string($conn, $name);
$ sql = "SELECT * FROM myTable WHERE name = '$name'";

This will ensure that the query string is not empty, even if $name contains single or double quotes.

Summary:

When using the mysqli_query function to execute a MySQL query, if the query string is empty, the error "PHP Warning: mysqli_query(): Empty query" will appear. This may be due to syntax errors, undefined variables, or MySQL connection errors, etc. To resolve this issue, you can check for syntax errors in the query string, make sure the MySQL server is running and connected correctly, use the mysqli_real_escape_string function to escape the variable to make sure the query string is not empty.

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