Oracle Database 12c Release 2 (12.2) includes a number of enhancements to datatype conversion functions, making it pretty easier to handle conversion errors.
Setup
The following table is used by the examples in this article.CREATE TABLE t1 (
data VARCHAR2(20)
);
INSERT INTO t1 VALUES ('11111');
INSERT INTO t1 VALUES ('01-JAN-2016');
INSERT INTO t1 VALUES ('AAAAA');
COMMIT;
CAST and TO_* Conversion Functions
In previous database versions failure during data type conversions resulted in an error.SELECT TO_NUMBER(data)
FROM t1;
ERROR:
ORA-01722: invalid number
no rows selected
SQL>
In Oracle database 12.2 the CAST function and several of the TO_* functions have been amended to include error handling functionality, allowing them to return a default value in the event of a conversion error.
FROM t1;
*
TO_NUMBER(DATADEFAULT-1ONCONVERSIONERROR)
-----------------------------------------
11111
-1
-1
SQL>
SELECT TO_DATE(data DEFAULT '01-JAN-2000' ON CONVERSION ERROR, 'DD-MON-YYYY' )
FROM t1;
TO_DATE(D
---------
01-JAN-00
01-JAN-16
01-JAN-00
SQL>
SELECT CAST(data AS TIMESTAMP DEFAULT NULL ON CONVERSION ERROR, 'DD-MON-YYYY')
FROM t1;
CAST(DATAASTIMESTAMPDEFAULTNULLONCONVERSIONERROR,'DD-MON-YYYY')
---------------------------------------------------------------------------
01-JAN-16 12.00.00.000000000 AM
SQL>
VALIDATE_CONVERSION Function
The VALIDATE_CONVERSION function is used to test if a conversion will be successful, making it possible to exclude data that would cause a problem during an operation. The function returns the value "1" if the conversion is successful and "0" if it fails.
FROM t1
WHERE VALIDATE_CONVERSION(data AS NUMBER) = 1;
DATA
--------------------
11111
SQL>
SELECT data
FROM t1
WHERE VALIDATE_CONVERSION(data AS DATE, 'DD-MON-YYYY') = 1;
DATA
--------------------
01-JAN-2016
SQL>