0
List two reasons why null values might be introducedin database?
Wiki User
∙ 11y ago
1. special requirements for its use in SQL joins.
2. special handling required by aggregate functions and SQL grouping operators
Wiki User
∙ 11y ago
Add your answer:
Earn +20 pts
What are the various reasons that lead to the occurrence of NULL values in relations?
A given field in a database table might be for a values that, in certain case, no such values exist or can be determined. For example, in an employee database, a field might be a foreign key to that employee's direct manager. However, in the case of the CEO, there is no such person. In that case, the field would be set to Null.
Why is quality of Data important?
There is a saying in the database industry - GIGO. It stands for garbage in Garbage out. The point of a database is to maintain data in a way that it has a use. For example, in a business a database might be used for inventory. What good would it be if the database didn't contain the right information on quantity and price. Also when you sell something you would like to have its quantity decremented in the database. If this didn't happen reliably you have a big problem. There are other factors in data quality that might be associated with the precision of the data. For example you might have a piece of data stored as an integer, but find out later that you actual need floating point for more precision in your queries.
What is a tuple in a database?
An arbitrary group of fields within a database record. Usually has some meaning in the context of the record. For example a 3-tuple in an address record might be the fields that contain the first, middle and last names of the person in the address field.
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.
Explain the possible reasons why the actual performance might be different from the budgeted performance?
TARC AFA students?
What are the various reasons that lead to the occurrence of NULL values in relations?
A given field in a database table might be for a values that, in certain case, no such values exist or can be determined. For example, in an employee database, a field might be a foreign key to that employee's direct manager. However, in the case of the CEO, there is no such person. In that case, the field would be set to Null.
When does one use an 'anime database'?
There are a number of reasons one might use an anime database. Some of these include to learn about new anime series and to research existing series and characters.
How do you check the data given by the user with database values using PHP from MySQL database?
You could use the string replace attribute but you might have to use Javascript, CGI, ASP or another scripting language to do so.
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). --
What organisations might use a database?
Banks
Is possible that during the physical database design and creation step of database development you might want to return to logical database design activity?
There are many reasons why this could occur, Just a few: Changes or clarification of user requirements Expansion of project scope Budgetary constraints invalidating original assumptions Testing demonstrating unacceptable query processing time
What is a field that might be used in a database about students?
A field that might be used in a database about students is "student ID," which is a unique identifier for each student in the database.
What is a database filter?
Filtering is the act of removing unwanted values from a result set. For example, if you have a database with 10,000,000 phone numbers, you might want only the phone numbers in the 215 area code, or only the phone numbers of clients that have purchased at least $500 in the past 12 months.
Why might the police use a database?
to find out others details
Why might someone have a Koi pond?
There are many reasons why might have a Koi pond. One might have a Koi pond for religious reasons, spiritual reasons, or simply for decoration purposes.
Who might help you identify your values.?
Your values are embodied in what you practice daily. You might best come to more precisely define your values by auditing where your time goes for a week or so.
Where can one find a large database of stock photos?
A local office supply store might have large database of stock photos but there would probably be a charge. There are other places where one might locate a large database of stock photos but this would require some research.
