What are the advantages and disadvantages of using UNION versus multiquery for retrieving data from multiple tables in PHP?

When retrieving data from multiple tables in PHP, using UNION can be advantageous as it allows you to combine the results of multiple SELECT statements into a single result set. This can simplify your code and make it more efficient. However, using UNION can also be less efficient than using multiquery, as it may require additional processing to combine the results. Multiquery can be advantageous when you need to execute multiple queries sequentially and process the results individually. 

// Using UNION to retrieve data from multiple tables
$query = "SELECT column1 FROM table1
          UNION
          SELECT column2 FROM table2";
$result = mysqli_query($connection, $query);

while ($row = mysqli_fetch_assoc($result)) {
    // Process the results
}
```

```php
// Using multiquery to retrieve data from multiple tables
$query1 = "SELECT column1 FROM table1";
$query2 = "SELECT column2 FROM table2";

mysqli_multi_query($connection, $query1);
mysqli_next_result($connection);
mysqli_multi_query($connection, $query2);

$result1 = mysqli_store_result($connection);
$result2 = mysqli_store_result($connection);

while ($row = mysqli_fetch_assoc($result1)) {
    // Process the results from table1
}

while ($row = mysqli_fetch_assoc($result2)) {
    // Process the results from table2
}

Keywords

UNION multiquery data retrieval multiple tables PHP

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