Checking for No Rows in MariaDB SELECT Queries (Prepared Statements)

2024-07-27

Using rowCount:
Using FOUND_ROWS (if applicable):
- This method is useful if you're using a LIMIT clause in your query. Add SQL_CALC_FOUND_ROWS before SELECT in your prepared statement. This tells MariaDB to keep track of the total number of rows that would have been returned without the LIMIT.
- After executing the statement, use the connection.serverVersion >= 100300 && (rowCount = 0 || connection.getFoundRows() > rowCount) (replace connection with your connection object and adjust for your language) to check if no rows matched the criteria.

Key Points:

Directly checking for zero rows within the prepared statement isn't possible in MariaDB's SQL language.
rowCount reflects the number of rows retrieved after applying filters (like WHERE clause).
FOUND_ROWS is helpful when you want to know the total number of rows before applying LIMIT.

import mysql.connector

# Connect to MariaDB
connection = mysql.connector.connect(host="localhost", user="your_username", password="your_password", database="your_database")

# Prepare the statement (replace with your actual query)
query = "SELECT * FROM users WHERE username = ?"
stmt = connection.cursor().prepare(query)

# Bind your parameter(s)
username = "test_user"
stmt.execute((username,))

# Check if any rows were found
result = stmt.fetchall()
if not result:
  print("No rows found")

# Close connection
connection.close()

Using FOUND_ROWS (example in PHP):

<?php

$conn = new mysqli("localhost", "your_username", "your_password", "your_database");

// Prepare the statement with SQL_CALC_FOUND_ROWS
$stmt = $conn->prepare("SELECT SQL_CALC_FOUND_ROWS * FROM users WHERE username = ?");
$stmt->bind_param("s", $username);
$username = "test_user";

// Execute the statement
$stmt->execute();

// Get the number of rows retrieved
$stmt->store_result();
$rowCount = $stmt->num_rows;

// Check for total rows using FOUND_ROWS
$totalRows = $conn->query("SELECT FOUND_ROWS()")->fetch_row()[0];

if ($rowCount === 0 && $totalRows > 0) {
  echo "No rows matched the criteria";
}

// Close connection
$stmt->close();
$conn->close();

?>

This approach relies on checking if the result set returned by the prepared statement is empty after execution. Here's how it works:

# After executing the prepared statement
result = stmt.fetchall()

if not result:
  print("No rows found")

This is a simple and widely applicable method. However, it doesn't differentiate between zero rows and an error during execution (which might also return an empty result set).

Using FETCH_ALL with exception handling:

This method attempts to fetch all rows using fetchall() and handles potential exceptions that might occur if no rows are present.

try:
  # Execute the prepared statement
  stmt.execute()

  # Attempt to fetch all rows
  result = stmt.fetchall()

  # If successful, rows were found (handle results)
  # ...

except Exception as e:
  # Exception might indicate no rows or other errors
  if "no data returned" in str(e).lower():  # Adjust for your language
    print("No rows found")
  else:
    # Handle other potential errors
    print(f"Error: {e}")

This approach provides more control over error handling, but adds complexity compared to a simple empty check.

Counting Rows in a Separate Query (if applicable):

This method involves creating a separate query to count the number of rows that would match the criteria. It's useful when you need the exact count:

# Prepare the original statement (replace with your query)
original_stmt = "SELECT * FROM users WHERE username = ?"

# Prepare a separate statement to count rows
count_stmt = connection.cursor().prepare("SELECT COUNT(*) FROM users WHERE username = ?")

# Use the same parameter for both statements
username = "test_user"
original_stmt.execute((username,))
count_stmt.execute((username,))

# Check the count
count_result = count_stmt.fetchone()
if count_result[0] == 0:
  print("No rows found")

# Close connections (not shown for brevity)