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How to Debug Date Related Problems Like (but not Limited to) ORA-01843, ORA-01821, ORA-1801 (Doc ID 338832.1)

Last updated on JUNE 13, 2023

Applies to:

Oracle Database - Enterprise Edition - Version and later
Oracle Database - Standard Edition - Version and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform. Oracle Server Enterprise Edition - Version: to


Help to debug date related problems like ORA-01843, ORA-01821, ORA-1801.


Anyone encountering an error that is date related.


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In this Document
 1) Common reasons for ORA-01843: not a valid month or ORA-01821: date format not recognized
 1.A) using a wrong date format mask in your code
 1.B) Using implicit date format masks (correct mask is set at "database level" but not used).
 1.C) Using TO_DATE on an text string.
 2) General steps to debug the error message:
 2.A) Compare Listener and database versions.
 2.B) Check ORA_NLSxx
 2.C) Set an event to know on what statement the error is happening.
 2.C.1)To define an event non persistent (=gone after restart of database) but no need to restart the database:
 2.C.2) To define the event persistent:
 3) Checking the client's settings.
 4) When using JDBC.
 5) Using after logon triggers.
 5.A) To enforce a value from the server side.
 5.B) To log clients settings.
 6) Getting wrong result (for example year 0014 is stored when string is using YY format like 14 ) of implicit or explict cast to a date dataype
 7) errors like ORA-01830: date format picture ends before converting entire input string (or other ora-018xx errors) after upgrade of the database
 8) Other possible causes (less likely):
 9) Known bugs:
 10) List of all ora-018xx errors and their event , usefull to set if you have "random" date errors

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