How to Perform Conditional Joins with Dynamic Table Names in MySQL?

Conditional Join with Dynamic Table Names in MySQL

In MySQL, it's possible to execute joins based on conditional criteria, allowing you to merge data from different tables dynamically. Consider the following scenario where you have a table containing 'type' column with enumerated values representing the names of other tables.

Your goal is to perform a join with a specific table based on the value in the 'type' column. For instance:

switch($type) {
  case 'table1':
    JOIN table1;
    break;
  case 'table2':
    JOIN table2;
    break;
}

Solution

Unfortunately, MySQL does not support conditional joins directly using a switch case syntax. However, you can achieve similar functionality using a combination of CASE and LEFT JOIN statements. The following query demonstrates this approach:

SELECT
  t.id,
  t.type,
  t2.id AS id2,
  t3.id AS id3
FROM t
LEFT JOIN t2 ON t2.id = t.id AND t.type = 't2'
LEFT JOIN t3 ON t3.id = t.id AND t.type = 't3'

In this query, the CASE statement is replaced with a series of LEFT JOIN operations. The ON clause for each LEFT JOIN specifies the join condition based on the value of the 'type' column.

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