A non-unique index exists on this column.

[Kumar38]

When I try to mark a column on parent table as Unique. IT throws below error . Deleted unique fields on Childs and updated data in column to make sure its unique. Tried setting index as true too

A non-unique index exists on this column. To create a unique index for this column use IndexCreator in the Tables & Columns  page or in this column's Table  record

[Hayo Lubbers]

@Kumar38 , can you add the screenshot and at least the table it is about (and if it extends something, the parent, like task)?

[Kumar38]

The parent and child all are custom tables. Parent doesn’t extend any table. Field is string field used for auto numering

[Hayo Lubbers]

Have a look at https://www.servicenow.com/community/platform-analytics-articles/get-duplicate-records-from-any-tabl.... This way you can get the existing duplicates out of the system.

If the index is not being created, because it says non-unique, there must be a duplicate somewhere.

As background script, delivering something like :

*** Script: INC0008111,INC0009009

gs.info(getDuplicates('incident','number')); //your table and fieldname

function getDuplicates(table, field) {
	var dupRecords = [];
	var gaDupCheck = new GlideAggregate(table);
	gaDupCheck.addAggregate('COUNT', field);
	gaDupCheck.addNotNullQuery(field);
	gaDupCheck.groupBy(field);
	gaDupCheck.addHaving('COUNT', '>', 1);
	gaDupCheck.query();
	while (gaDupCheck.next()) {
		dupRecords.push(gaDupCheck[field].toString());
	}
	return dupRecords;
}