Question

Recently I copied an Oracle database from one machine to another.

1. Original: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0
2. Copy: Oracle Database 11g Express Edition Release 11.2.0.2.0 – Production
   For some reason the following query works on the original but not on the copy.

If a t.tdt_id is substituted in place of tdt_id in the group by the query works (as per td_tablespaces t )

Can someone explain why this is and if it has something to do with the installation. The data is the exact same in both.

SELECT
    tdt_name as "name", 
    tdt_contents as "Content",         
    tdt_status as "Status",         
    round(( subsize.SubSize_MB ), 2 ) as "size used",         
    round(( sum( MaxMB ) - subsize.SubSize_MB ), 2 ) as "size free" 
FROM    
    td_tablespaces t 
INNER JOIN        
    (
        SELECT 
            tdt_id,
            CASE 
                 WHEN upper( d.df_autoextend ) = 'YES' THEN  round(( sum( df_maxsize ) / 1024 ), 2 )  
                 WHEN upper( d.df_autoextend ) = 'NO' THEN round(( Sum( df_size ) / 1024 ), 2 )                 
            END as MaxMB
        FROM    
            td_datafiles d         
        GROUP BY 
            tdt_id,                 
            d.df_autoextend,                 
            df_maxsize,                 
            df_size         
    ) sub 
ON      
    t.tdt_id = sub.tdt_id 
INNER JOIN        
    (
        SELECT 
            tdt_id,                 
            sum( df_size / 1024 ) -( df_free / 1024 ) SubSize_MB,                 
        df_free      / 1024 SubSize_Free         
        FROM    
            td_datafiles df         
        GROUP BY 
            tdt_id,                 
            df_free         
    ) subsize 
ON 
    t.tdt_id = subsize.tdt_id 
WHERE 
    ins_id   = 2096 
GROUP BY 
    tdt_id,         
    tdt_name,         
    tdt_contents,        
    tdt_status,         
    subsize.SubSize_MB,         
    SubSize_Free 
ORDER BY tdt_contents  

Answer 1

Oracle enforces strict rules when referencing columns in a query and will raise ORA-00918: column ambiguously defined if a column is found on two tables and referenced without a table prefix or an alias.

Since tdt_id is defined both in t and subsize, you couldn’t call tdt_id without an alias or a table name in:

• the SELECT clause
• the WHERE clause
• the ORDER BY clause

For some reason in some versions of 10g the error is not raised when the column is in a GROUP BY clause. This is inconsistent with the rest of the syntax parsing, this could lead to ambiguous results and must have been classified as a bug. This has been corrected in 11g.