SQL INTERVIEW QUESTION & ANSWERS
| 76. |
What does a null value signify? |
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A null signifies that a value is undefined or not known. This is not the same as a zero, a blank, or a default value. Instead, it indicates that a data value is absent. |
| 77. |
What command is used to retrieve the results after a cursor has been opened? |
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The FETCH command |
| 78. |
What is a UNIQUE KEY? |
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A UNIQUE KEY is one or more columns that must be unique for each row of the table. |
| 79. |
What is a FOREIGN KEY? |
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A FOREIGN KEY is one or more columns whose values are based on the PRIMARY or CANDITATE KEY values from the database. |
| 80. |
What is a CANDIDATE KEY? |
| |
CANDIDATE KEY is a minimal superkey. A candidate key for a relation schema
is a minimal set of attributes whose values uniquely identify tuples in the corresponding relation. |
