COMPUTER SCIENCE AND ENGINEERING
SQL
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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A NULL value means zero.
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A null value can only be used with numeric attributes.
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Null value just means that data of that attribute is not available.
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None of these.
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Detailed explanation-1: -A NULL value means zero. A null value can only be used with numeric attributes. Null value just means that data of that attribute is not available.
Detailed explanation-2: -What is a NULL value? A NULL value is a special marker used in SQL to indicate that a data value does not exist in the database. In other words, it is just a placeholder to denote values that are missing or that we do not know.
Detailed explanation-3: -A null value in a relational database is used when the value in a column is unknown or missing. A null is neither an empty string (for character or datetime data types) nor a zero value (for numeric data types).
Detailed explanation-4: -According to the three-valued logic of SQL, the result of null = null is not true but unknown. SQL has the is [not] null predicate to test if a particular value is null .
Detailed explanation-5: -NULL values are used when you want the records that don’t have a value. NOT NULL values represent missing or unknown data. A table column by default holds NULL values. NULL values are used when you want records to have a value.