Multiple choice technology databases

How many columns are there in dual table?

  1. 1

  2. 2

  3. >1

  4. N
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A Correct answer
Explanation

Oracle's DUAL table has exactly one column named DUMMY of type VARCHAR2(1). This special table is used for selecting constant expressions or performing calculations when no actual table is needed. It always contains one row with value 'X'. The single column design allows SELECT statements to return scalar values.

AI explanation

Oracle's DUAL table has exactly one column, named DUMMY (a VARCHAR2(1) containing the value 'X'), and exactly one row. It exists purely as a convenience table for evaluating expressions or calling functions that don't need real table data (e.g., SELECT SYSDATE FROM DUAL). The other options (2, >1, N) don't reflect DUAL's actual minimal single-column, single-row structure.

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