edb_redwood_strings v15

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About string display after concatenation

In Oracle, when a string is concatenated with a null variable or null column, the result is the original string. However, in PostgreSQL, concatenation of a string with a null variable or null column gives a null result.

If the edb_redwood_strings parameter is set to TRUE, the concatenation operation results in the original string as done by Oracle. If edb_redwood_strings is set to FALSE, the native PostgreSQL behavior is maintained.

Example

The sample application contains a table of employees. This table has a column named comm that's null for most employees. The following query is run with edb_redwood_string set to FALSE. The concatenation of a null column with non-empty strings produces a final result of null, so only employees that have a commission appear in the query result. The output line for all other employees is null.

SET edb_redwood_strings TO off;

SELECT RPAD(ename,10) || ' ' || TO_CHAR(sal,'99,999.99') || ' ' ||
TO_CHAR(comm,'99,999.99') "EMPLOYEE COMPENSATION" FROM emp;
Output
    EMPLOYEE COMPENSATION
----------------------------------

 ALLEN        1,600.00     300.00
 WARD         1,250.00     500.00

 MARTIN       1,250.00   1,400.00




 TURNER       1,500.00        .00




(14 rows)

The following is the same query executed when edb_redwood_strings is set to TRUE. Here, the value of a null column is treated as an empty string. The concatenation of an empty string with a non-empty string produces the non-empty string. This result is consistent with the results produced by Oracle for the same query.

SET edb_redwood_strings TO on;

SELECT RPAD(ename,10) || ' ' || TO_CHAR(sal,'99,999.99') || ' ' ||
TO_CHAR(comm,'99,999.99') "EMPLOYEE COMPENSATION" FROM emp;
Output
   EMPLOYEE COMPENSATION
----------------------------------
SMITH          800.00
ALLEN        1,600.00     300.00
WARD         1,250.00     500.00
JONES        2,975.00
MARTIN       1,250.00   1,400.00
BLAKE        2,850.00
CLARK        2,450.00
SCOTT        3,000.00
KING         5,000.00
TURNER       1,500.00        .00
ADAMS        1,100.00
JAMES          950.00
FORD         3,000.00
MILLER       1,300.00
(14 rows)
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