How to Convert Complex MySQL Queries with Multiple Statements to Laravel Eloquent?

Converting Complex MySQL Queries with Multiple Statements to Laravel Eloquent

In the world of database querying, the ability to convert intricate SQL queries to their Laravel Eloquent counterparts is crucial. One such challenge arises when dealing with multi-statement MySQL queries, which involve a series of statements such as PREPARE, EXECUTE, and DEALLOCATE.

Problem Statement

You have a MySQL query with multiple statements:

SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'ifnull(SUM(case when location_code = ''',
      location_code ,
      ''' then quantity end),0) AS `',
      location_code , '`'
    )
  ) INTO @sql
FROM
  item_details;
SET @sql = CONCAT('SELECT item_number,SUM(quantity) as "total_quantity", ', @sql, ' 
                  FROM item_details
                   GROUP BY item_number');

PREPARE stmt FROM @sql;
EXECUTE stmt;

DEALLOCATE PREPARE stmt;

You're looking to convert this complex query to Laravel Eloquent, but you're unsure how to handle the multiple statements involved.

Solution

While some aspects of the MySQL query, such as the preparation and execution of the statement, are not directly translatable to Eloquent, the core functionality can be achieved. Here's a solution:

<code class="php">DB::table('item_details')
    ->selectRaw('GROUP_CONCAT(...) INTO @sql')
    ->get();

$sql = DB::selectOne('select @sql')
    ->{'@sql'};

ItemDetails::select('item_number', DB::raw('SUM(quantity) as total_quantity'))
    ->selectRaw($sql)
    ->groupBy('item_number')
    ->get();</code>

Explanation

This solution is a blend of Eloquent and raw SQL queries.

• DB::table('item_details')->selectRaw('GROUP_CONCAT(...) INTO @sql')->get(); executes the first statement, which creates a temporary SQL variable named @sql.
• $sql = DB::selectOne('select @sql')->{'@sql'}; retrieves the value of the @sql variable and stores it in the $sql variable.
• ItemDetails::select('item_number', DB::raw('SUM(quantity) as total_quantity'))->selectRaw($sql)->groupBy('item_number')->get(); constructs the main Eloquent query. It uses selectRaw($sql) to insert the dynamic SQL string obtained from $sql.

This approach allows you to perform the complex MySQL query within the context of Laravel Eloquent, simplifying your code and maintaining maintainability.

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