[Solved] Why doesn\'t this query fail, when converting to_date

How to optimize this SQL query?

In case you have your own slow SQL query, you can optimize it automatically here.

For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:

  1. Description of the steps you can take to speed up the query.
  2. The optimal indexes for this query, which you can copy and create in your database.
  3. An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
  1. Avoid Subqueries (query line: 22): We advise against using subqueries as they are not optimized well by the optimizer. Therefore, it's recommended to join a newly created temporary table that holds the data, which also includes the relevant search index.
The optimized query:
SELECT
        DISTINCT TO_CHAR(START_DATE,
        'MM/DD/YYYY'),
        TO_CHAR(END_DATE,
        'MM/DD/YYYY') 
    FROM
        (SELECT
            START_DATE,
            END_DATE,
            END_DATE - START_DATE 
        FROM
            (SELECT
                TO_DATE(SUBSTR(B,
                1,
                10),
                'MM/DD/YYYY') START_DATE,
                TO_DATE(SUBSTR(B,
                14,
                10),
                'MM/DD/YYYY') END_DATE 
            FROM
                (SELECT
                    'test date' b 
                FROM
                    dual)) 
            WHERE
                END_DATE - START_DATE != 6)

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* original question posted on StackOverflow here.