## -6001: Duplicate column name

### Explanation:

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1. The column names of a table must differ from each other. Base tables without user-defined key columns and named result tables contain the implicitly created column SYSKEY.

2. Named result tables with columns which have not been explicitly named and which do not inherit a column name from the underlying base table implicitly get the column name "EXPRESSION_", where _ stands for a positive integer.

3. A column must not be specified more than once in an INSERT or UPDATE statement or in a sequence of key specifications.

### User Action:

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1. Use different column names.

2. In a CREATE VIEW or QUERY statement, uniqueness of column names can be achieved by specifying reference names in the selected columns. In a CREATE VIEW statement, uniqueness can also be obtained by specifying alias names.

3. Correct the repeated specification of the same column.