


How to Resolve Oracle's ORA-00918: Ambiguous Column Definition Error in SELECT * Queries?
Jan 13, 2025 pm 09:26 PM*Oracle ORA-00918: Ambiguous Column Definition – A SELECT Query Problem**
Running a SELECT *
query against multiple joined tables in Oracle can lead to the dreaded ORA-00918 error: "ambiguous column definition." This happens when your query includes columns with identical names from different tables. Oracle can't determine which column you intend to retrieve.
Here's an example query that often triggers this error:
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 <= 25
The Root of the Problem
The SELECT *
attempts to retrieve all columns, but since id
exists in multiple tables (coaches
, people
, users
), Oracle is left uncertain which id
column to select.
The Solution: Precise Column Specification
To fix ORA-00918, avoid SELECT *
. Instead, explicitly list the columns you need. There are two primary ways to achieve this:
1. Direct Column Selection
Specify each column using its fully qualified name (table.column):
SELECT coaches.id, people.name, users.username, coaches.team 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 <= 25
2. Utilizing Column Aliases
Assign unique aliases to columns with the same name using the AS
keyword:
SELECT coaches.id AS coaches_id, people.name AS person_name, users.username AS user_username, coaches.team AS coaches_team 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 <= 25
By employing either method, you provide Oracle with unambiguous instructions, resolving the ORA-00918 error and ensuring your query executes successfully. Remember to replace the example column names with your actual column names.
The above is the detailed content of How to Resolve Oracle's ORA-00918: Ambiguous Column Definition Error in SELECT * Queries?. For more information, please follow other related articles on the PHP Chinese website!

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