Why Does My SQL Query Fail with a 'Column Does Not Exist' Error Even Though the Column Exists?

Troubleshooting SQL query error "column does not exist"

When executing a SQL query, you may encounter a "column does not exist" error. This is especially puzzling when the column appears to exist in the table's definition.

Example scene

Consider the following query:

select sim.id as idsim, 
       num.id as idnum 
from main_sim sim 
  left join main_number num on (FK_Numbers_id=num.id);

This query attempts to retrieve data from two tables main_sim and main_number based on the FK_Numbers_id foreign key relationship. However, when executing the query, I receive the following error:

<code>ERROR:  column "fk_numbers_id" does not exist</code>

Solution

After checking the table definition using the command d main_sim you will notice that the column exists, named FK_Numbers_id, and not the fk_numbers_id specified in the query.

dbMobile=# \d main_sim

...
FK_Numbers_id   | integer               | 

Explanation

In this case, the column names are case-sensitive because the table definition uses double quotes. Therefore, column references in queries must also use double quotes to match the exact case of the column name.

Corrected query

To resolve this issue, please modify the query as follows:

select sim.id as idsim, 
       num.id as idnum 
from main_sim sim 
  left join main_number num on ("FK_Numbers_id" = num.id);

This corrected query uses double quotes around the column names in the LEFT JOIN clause, ensuring a correct match to the table definition. By adjusting the column references to match the exact case of the column names, the query will now execute successfully.

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