Real time issue in Teradata

This error will happen when you update the target with multiple rows from the source.
If you defined primary index field for your target and if you defined those fileds in update query condition, this error will be obvious one.

For example,

UPDATE tbl_emp
FROM
(SELECT
id,
name
FROM tbl_dept) DEPT
SET name = DEPT.name
WHERE
tbl_emp.id = DEPT.id;

In the above code, if tbl_dept has non-unique values and tbl_emp is a set table, then the error will appear.

Solution:
You can render the query with DISTINCT in the select query.

UPDATE tbl_emp
FROM
(SELECT DISTNCT
id,
name
FROM tbl_dept) DEPT
SET name = DEPT.name
WHERE
tbl_emp.id = DEPT.id;