Duplicate constraints check/not null
Recently we did a refresh from production database to UAT database using exp/imp utility. General practise is to take 2 export dump. One by listing the table names and other by schemawise export with "rows=n" option. Similarly at the time of import, first the data dump (only tables/indexes/constraints) was imported and then from the export dump (with ignore=y) which was taken using "rows=n". In general, we use to import the no data dump (taken with rows=n) few times with options like constraints=n, grants=n etc.
Following issue was identified,
For few tables, the check/not null constraints gets duplicated whenever the no-data dump is imported. I checked for one table, If I describe that table, then "not null" is displayed only for one column and this column holds the primary key constraint. But in dba_constraints or dba_con_columns, there were many entries with constraint type as "C" and the search condition is "xxxxxxx" is not null. This gets repeated for the same table with different constraint name. Whenever I do no-data import, additional constraints get created for the same column with different constraint name. But, in "desc <table name>", these columns