How to Execute Multiple SQL Queries in a Single Result Set with PHP/MySQL?

Executing Multiple Queries in PHP/MySQL

Question:

How can I combine multiple SQL queries into a single result set in PHP using MySQL?

Answer:

To execute multiple concatenated queries in PHP using MySQL, follow these steps:

1. Create the SQL Statement:
   Concatenate the individual SQL queries into a single string, separated by semicolons (;). Ensure there are two semicolons at the end of each query except the last one.
2. Connect to Database:
   Use the mysqli_connect function to establish a database connection.
3. Prepare Query:
   Use the mysqli_prepare function to prepare the multiple-query statement.

$query = "SQL STATEMENT 1;;SQL STATEMENT 2;;SQL STATEMENT 3";

4. Execute Queries:
   Use the mysqli_multi_query function to execute the prepared statement.

if (mysqli_multi_query($link, $query)) {
    do {
        // Store and process results
    } while (mysqli_next_result($link));
}

5. Fetch Results:
   After executing the queries, use the mysqli_fetch_array to retrieve results from each query.

Example:

$link = mysqli_connect("server", "user", "password", "database");

$query = "CREATE VIEW current_rankings AS SELECT * FROM main_table WHERE date = X;;
CREATE VIEW previous_rankings AS SELECT rank FROM main_table WHERE date = date_sub('X', INTERVAL 1 MONTH);;
CREATE VIEW final_output AS SELECT current_rankings.player, current_rankings.rank as current_rank LEFT JOIN previous_rankings.rank as prev_rank
             ON (current_rankings.player = previous_rankings.player);;
SELECT *, @rank_change = prev_rank - current_rank as rank_change from final_output";

if (mysqli_multi_query($link, $query)) {
    do {
        if ($result = mysqli_store_result($link)) {
            while ($row = mysqli_fetch_array($result)) {
                // Process results
            }
            mysqli_free_result($result);
        }
    } while (mysqli_next_result($link));
}

Alternative Approach:

Alternatively, you can execute each query separately and process the results one by one. This approach is recommended if the queries are not interdependent.

$query1 = "Create temporary table A select c1 from t1";
$result1 = mysqli_query($link, $query1);

$query2 = "select c1 from A";
$result2 = mysqli_query($link, $query2);

while($row = mysqli_fetch_array($result2)) {
    // Process results
}

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