Oracle ORA_DST_ERROR Function: A Simple Guide

The ORA_DST_ERROR function in Oracle SQL is another highly specialized diagnostic tool used by Database Administrators (DBAs). It is part of the toolkit for managing database time zone file upgrades, along with ORA_DST_AFFECTED and ORA_DST_CONVERT.

While ORA_DST_AFFECTED gives a simple "yes" (1) or "no" (0) answer, ORA_DST_ERROR is more specific. It tells you exactly what kind of error a timestamp will cause under the new time zone rules.

What is the ORA_DST_ERROR Function in Oracle?

The ORA_DST_ERROR function checks a TIMESTAMP WITH TIME ZONE value against the new time zone file (during an upgrade) and returns a numeric code indicating the specific error.

It returns one of three values:

• 0: The timestamp is valid and causes no error.
• 1878: This is a "nonexisting time" error. This typically happens during a "spring forward" for Daylight Saving Time, when an hour is skipped (e.g., the clock jumps from 1:59 AM to 3:00 AM).
• 1883: This is a "duplicate time" error. This typically happens during a "fall back," when an hour is repeated (e.g., the clock goes from 1:59 AM back to 1:00 AM).

This function is the primary diagnostic tool DBAs use to find why data is affected by a DST change.

ORA_DST_ERROR Function Syntax

The syntax for ORA_DST_ERROR is:

ORA_DST_ERROR(timestamp_with_time_zone_expr)

Let's break that down:

• timestamp_with_time_zone_expr: The TIMESTAMP WITH TIME ZONE value or column you want to check.

Important: This is a DBA-Only Function

Like its companions, this function cannot be run in a normal SQL session. It is designed to be run only during a specific database maintenance window.

If you try to run it, you will get an ORA-30190 error: ORA-30190: ORA_DST_ERROR can be issued only during a TSTZ upgrade

A DBA must first start the upgrade process (e.g., by running DBMS_DST.BEGIN_PREPARE or DBMS_DST.BEGIN_UPGRADE) before this function becomes active.

The examples below are conceptual and show how a DBA would use them during that maintenance process.

Oracle ORA_DST_ERROR Function Examples

Example 1: Diagnosing All Affected Data with ORA_DST_ERROR

This is the most common use case. A DBA wants to find all rows that have a problem and categorize them by the type of problem.

Query (Run by DBA during DST upgrade):

-- Find all rows that need to be fixed and categorize the error
SELECT
  event_id,
  event_time,
  ORA_DST_ERROR(event_time) AS "Error_Code"
FROM
  events
WHERE
  ORA_DST_AFFECTED(event_time) = 1;

Result: (The query would return a list of all invalid timestamps and their specific error code.)

EVENT_ID   EVENT_TIME                           Error_Code
---------- ------------------------------------ ----------
101        23-MAR-25 02.15.00.00 AM US/EASTERN   1878
102        02-NOV-25 01.30.00.00 AM US/EASTERN   1883

This tells the DBA that event 101 is a "nonexisting time" and event 102 is a "duplicate time."

Example 2: Using ORA_DST_ERROR in a CASE Statement for a Report

A DBA can use ORA_DST_ERROR in a CASE statement to generate a human-readable report of all time zone problems before attempting to fix them.

Query (Run by DBA during DST upgrade):

-- Create a human-readable report of all errors
SELECT
  event_id,
  event_time,
  CASE ORA_DST_ERROR(event_time)
    WHEN 1878 THEN 'Non-existing time (Spring forward)'
    WHEN 1883 THEN 'Duplicate time (Fall back)'
    ELSE 'No Error'
  END AS "Error_Type"
FROM
  events
WHERE
  ORA_DST_ERROR(event_time) <> 0;

Result:

EVENT_ID   EVENT_TIME                           Error_Type
---------- ------------------------------------ --------------------------------
101        23-MAR-25 02.15.00.00 AM US/EASTERN   Non-existing time (Spring forward)
102        02-NOV-25 01.30.00.00 AM US/EASTERN   Duplicate time (Fall back)