What are common pitfalls to avoid when using UNION in MySQL queries for PHP applications?

One common pitfall to avoid when using UNION in MySQL queries for PHP applications is to ensure that the number of columns selected in each query within the UNION statement is the same. If the number of columns differs, it can lead to errors or unexpected results. To fix this, make sure to select the same number of columns in each query within the UNION statement. 

$query = "SELECT column1, column2 FROM table1
          UNION
          SELECT column1, column2 FROM table2";
$result = mysqli_query($connection, $query);

Keywords

UNION MySQL queries PHP applications SQL injection data validation

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