How to Resolve ORA-00918: 'column ambiguously defined' in SQL SELECT * Queries?

*Oracle Error ORA-00918: Resolving Ambiguous Columns in SELECT Statements**

Executing a SELECT * query involving multiple tables with identically named columns often results in the ORA-00918 error: "column ambiguously defined." This ambiguity arises because the database cannot determine which table's column to retrieve when multiple tables share a column name.

Consider this example:

<code class="language-sql">SELECT *
FROM
  (SELECT DISTINCT(coaches.id),
    people.*,
    users.*,
    coaches.*
  FROM "COACHES"
  INNER JOIN people ON people.id = coaches.person_id
  INNER JOIN users ON coaches.person_id = users.person_id
  LEFT OUTER JOIN organizations_users ON organizations_users.user_id = users.id
) WHERE rownum <p>To correct this, replace the ambiguous `SELECT *` with a specific column selection.  For instance:</p><p>Instead of selecting all columns (`SELECT *`), explicitly list the desired columns and use aliases to resolve ambiguity:</p>SELECT
  coaches.id AS COACHES_ID,
  people.name,
  users.email,
  coaches.team
FROM ...  -- Rest of your query remains the same

This approach assigns unique aliases (e.g., `COACHES_ID`) to each selected column, eliminating the ambiguity.  Alternatively, omit duplicate columns entirely, selecting only the necessary data.

Best practice dictates avoiding `SELECT *` in production SQL.  Explicitly defining columns enhances code clarity, maintainability, and reduces the risk of errors caused by ambiguous column names.</code>

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