RE: What is the data type of the column of Dual table?
The DUAL table is owned by the user SYS and can be accessed by all users. It contains one column DUMMY and one row with the value X. The DUAL table is useful when you want to return a value once only: for instance the value of a constant pseudocolumn or expression that is not derived from a table with user data. The DUAL table is generally used for SELECT clause syntax completeness because both SELECT and FROM clauses are mandatory and several calculations do not need to select from actual
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