Using the Same IN-Statement with Multiple Columns

Introduction

When working with databases, it’s not uncommon to need to perform complex queries that filter rows based on multiple conditions. One common technique is using the IN operator, which allows you to specify a list of values that must be present in a column for a row to be included in the results.

In this article, we’ll explore how to use the same IN statement with different values across multiple columns. We’ll dive into the syntax, examples, and common pitfalls to help you optimize your queries and avoid warnings like “mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in…”.

Background on the IN Operator

The IN operator is used to filter rows based on a list of values. When using IN, the database engine checks if any value from the specified list exists in the column being tested. If a match is found, the row is included in the results.

For example, consider a table with columns Name and Age. Suppose you want to retrieve all rows where Age is between 20 and 30 (inclusive). You can use the following query:

SELECT * 
FROM Members 
WHERE Age IN (20, 21, 22, ..., 30);

This query will return all rows where Age matches any of the values in the specified list.

Using Multiple Columns with the Same IN-Statement

Now, let’s discuss how to use the same IN statement with different values across multiple columns. The key insight is that you can’t nest the IN operator within another column. Instead, you must use a separate IN clause for each column.

Consider the following example:

$sql = "SELECT * FROM Mitglied 
        WHERE Vorname IN ('$sql_eingabe') OR Name IN ('$sql_eingabe')";

This query will return all rows where either Vorname or Name matches $sql_eingabe.

However, when adding another column to the query, the syntax breaks:

$sql = "SELECT * FROM Mitglied 
        WHERE (Vorname, Name) IN (($sql_eingabe), ($sql_eingabe))";

This query will not work as expected because the IN operator is being used incorrectly. The warning message you receive is likely due to a mismatch between the return type of the IN function and the expected parameter type.

Correct Syntax: Using Multiple OR Conditions

To fix this issue, we must use separate OR conditions for each column:

$sql = "SELECT * 
        FROM Mitglied 
        WHERE Vorname IN ('$sql_eingabe') OR Name IN ('$sql_eingabe')";

By using separate IN clauses for each column, you can ensure that the query returns all rows where either condition is met.

Additional Tips and Considerations

Here are a few additional tips to keep in mind when working with multiple columns and the IN operator:

Use parentheses: When using multiple conditions or complex logic, it’s essential to use parentheses to clarify the order of operations.
Avoid nesting: As we discussed earlier, you cannot nest the IN operator within another column. Instead, use separate OR conditions for each column.
Consider indexing: If you’re working with large datasets or frequently filtering rows based on multiple columns, consider creating indexes on the relevant columns to improve performance.
Test thoroughly: Always test your queries thoroughly to ensure they return the expected results and avoid warnings like “mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in…”.

Example Use Case: Retrieving Members with Specific Names or Surnames

Suppose you have a table called Members with columns Name, Surname, and Age. You want to retrieve all members who have either the same first name as $sql_eingabe or the same surname as $sql_eingabe.

Here’s an example query that uses separate IN clauses for each column:

$sql = "SELECT * 
        FROM Members 
        WHERE Name IN ('$sql_eingabe') OR Surname IN ('$sql_eingabe')";

This query will return all rows where either the first name or surname matches $sql_eingabe.

Conclusion

Using multiple columns with the same IN statement requires careful syntax and consideration of column relationships. By following best practices, such as using separate OR conditions for each column, you can ensure that your queries return accurate results while avoiding warnings like “mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in…”.

Remember to test your queries thoroughly and consider optimizing performance by creating indexes on relevant columns. With practice and experience, you’ll become proficient in using multiple columns with the IN operator to optimize your database queries.

Additional Resources

If you’d like to learn more about database querying or improve your skills with MySQL or other databases, consider exploring the following resources:

Last modified on 2025-03-22