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In a database, there is a difference between an empty field and one whose value is undetermined. For example, an employee database might have value constraints defined that check any entry into a date field be a valid date. If one such field was for termination date, it couldn't be left blank because that's not a valid date but no valid date exists as yet. In such a case, setting the field to Null solves the problem.
A null value, in common usage, means completely empty or containing binary zero. Such values are used in many places. They can be used as string terminators, flags in code, and for various other programming uses.
According to Microsoft, however, null values are actually undefined and that no two null values are equal. Such values denote that the data is not applicable, unknown, or it serves as a placeholder for future data.
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Have foreign keys null values?
Yes Foreign key can have null value.
What are the various cases where use of a NULL value would be appropriate?
Optional data fields: NULL can be used to indicate that certain fields in a database can have no value assigned to them. Unknown data: NULL can be used to represent missing or unknown information. Default values: NULL can be used as a default value for a field until a proper value is provided. Uninitialized variables: In programming, NULL can be used to indicate that a variable has not been assigned a value yet.
Does foreign key alllows null values and duplicate values?
A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.A foreign can have null values and it can have duplicate values.
Null in programming?
in Russian Null means zero. in some languages Null is a macro for zero. in others Null is a single-tone object which referes to the value Null and thus could be compared to other values. Null has many names from nill Nill nil in diffrent languages. most of the time, Null is used to indicate, no value is set to a variable.
Why null values in database?
The 'null'-content of any given field is just that. It's a 'nothing'. Example, if you create a database to hold chemical values for instance. If the values are, for example, real nubers. That would imply that any value that has 0 in it, is just that; zero. It was beeing measured, and found to contain zero. On the other hand if a value was not tested, the value of that compound should be set to 'null'. If a 'null' value isn't supported by the database a workaround is to set 'null' values to -1 (as per the example above). --
Discuss the various reasons that lead to the occurrence of null values in relations?
If an instance (tuple) of a relation lacks having that attribute. i.e: a student that does not have a mobile phone or an office phones. The values for these attribute for that particular student will be null. It is important to note that a null value can mean either an unknown value, or a value that exists, but not yet available.
Can You insert a row containing a null attribute value using SQL?
Yes, you can insert a row with a null attribute value using SQL by simply not specifying a value for that attribute in the INSERT statement or explicitly using the keyword NULL. For example, if you have a column called "email" and want to insert a row without specifying an email value, you can do so by executing: INSERT INTO table_name (email) VALUES (NULL);
What is difference between null value and not null value?
In databases: Null Value: Represents the absence of a value or an unknown value. It indicates that the data is missing or not applicable. Not Null Value: Indicates that a field contains a valid, defined value. It means the data is present and has been explicitly set.
What are p values?
P values are a measure used in statistical hypothesis testing to determine the strength of evidence against the null hypothesis. A low p value (usually less than 0.05) suggests that there is strong evidence to reject the null hypothesis, indicating that there is a significant difference or effect.
What group function can be used to perform a count that includes NULL values?
You can not group a NULL value natively. You can however transform the NULL into so other unique value; dynamically, without writing this value to the database; and group by this. You would accomplish this by implementing a coalesce T-SQL expression For example lets say the MiddleName field is NULL in many cases and you want to to group by these.. You might want to turn this NULL into say an * for purposes of giving a value that you can group by. Now you can group by all MiddleName entries and also use a where clause to excluded those values <> * giving you a sub grouping of those records ONLY having null. The SQL command would look something like this: SELECT coalesce(MiddleName, '*') FROM YourTableNameHere WHERE MiddleName LIKE '*' GROUP BY MiddleName The coalesce returns the first NON NULL value in the chain(you can have more than two values). In the above example you will get the MiddleName if there is one and an * if the database value is NULL. This is a SELECT so there is NO update to the database.
What is the meaning of Null Null?
In mathematics, null mean zero value.-----------In mathematics, the null set is the set without any members that is contained in every set.In computing, null is used in some languages to mean 'no value'-in particular, not zero, not true and not false. (See, for example, SQL or PHP.)In statistics, the word 'null' is most often used in the term 'null hypothesis'. Usually a null hypothesis is a statement claiming that a population parameter of interest equals a certain value. Then the alternative hypothesis might be that the parameter assumes values other than that given value.Perhaps it may be said that the word null has various meanings, depending on context.
What are field can be used as primary key?
A field or set a of fields Êin a database tableÊwith unique values Êcan be used as a primary key.ÊPrimary key field cannot have a null value.
