0
In a database it can be 'not known' or 'not applicable'.
Wiki User
∙ 13y ago
Add your answer:
Earn +20 pts
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). --
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.
If null is compared with null what is the result-true or false or null or unknown?
You mean SQL? NULL = anything IS NULL NULL <> anything IS NULL ... NULL IS NULL = TRUE NULL IS NOT NULL = FALSE
What is the difference between an array shift and unsetting a variable in PHP?
By shifting the values in an array, you are moving a key's value to the previous key. The very first key's value is obliterated. By shifting all values in the array, all keys will have a value of NULL. Unsetting a variable is entirely different -- performing a variable unsetting causes the variable to have a value of NULL, as if it was never set.
C plus plus program of periodic table?
The Periodic Table Of Elements has a well defined order. The layout can be emulated easily since the arrangement is quite logical.The first step would be to define a struct containing the following members as a minimum:- atomic number (int - number of protons in its nucleus)- symbol (char* - short form of the element name)- name (char* - long form of the element name)i.e.:struct elementinfo {int atomicnumber;char *symbol, *name;};Other members can be added as your program develops.The next step is to arrange the table itself. If you're using Win32 or another graphical system, it's a matter of drawing a box (Win32 would require a MoveToEx() call and four LineTo() calls) and TextOut() (or a related function) for the atomic number and element symbol (centered horizontally and aligned top and bottom respectively).Including conio.h or curses.h would give you the ability to position the cursor and even change the text color, allowing for an alternate "graphical" method.To keep things simple, storing the elements in an array would require something akin to the following:struct elementinfo elementlist[]={{1, "H", "Helium"}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {2, "He", "Helium"},{-1, NULL, NULL},{3, "Li", "Lithium"}, {4, "Be", "Beryllium"}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{5, "B", "Boron"}, {6, "C", "Carbon"}, {7, "N", "Nitrogen"},{8, "O", "Oxygen"}, {9, "F", "Fluorine"}, {10, "Ne", "Neon"},{-1, NULL, NULL},...{-2, NULL, NULL}};In the above array, {0, NULL, NULL} represents a blank displayed for that particular cell, and {-1, NULL, NULL} represents a newline. The {-2, NULL, NULL} signifies the end of the table. The following for() loop would wrap around your display code like so:for (count=0; elementlist[count].atomicnumber!=-2; count++) {if elementlist[count].atomicnumber==-1) {// jump to next line of elements}else {// display current element}}Drawing this graphically, you'd have to keep track of the current cursor (X, Y) position.If you are sending this to stdout or another text stream (i.e. text file), you could draw each line, referencing the array of elements as you go. The list of elements would have to be stored in a nested array: the outermost array contains each line of elements in an array. This would do away with the {-1, NULL, NULL} terminating each line of elements.Extending this code to use classes would be relatively simple, but might only make sense if you were drawing this graphically storing each element as an object.The Lanthanides and Actinides, since they're displayed separately from the main table, would probably have to be stored separately for sake of convenience.Also, as laboratories continue to synthesize (or, on the rare chance, discover) new elements, the layout of the table may change (even drastically) to suit. Thus, the code would have to be altered accordingly.See the related links below for more ideas on how to design a program that displays the Periodic Table of Elements.(Note: Code originally posted was copyrighted. Added to related links.)
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.
Can a foreign key be null?
yes .a foreign key can have null values
Have foreign keys null values?
Yes Foreign key can have null value.
When was Null-A Three created?
Null-A Three was created in 1985.
Did Group functions include nulls in calculations?
no null values will not be included explanation when oracle parse the query the null values will be omitted for some reason if you want to consider null values you have to use some oracle functions like nvl or nvl2
Is the critical region the values of the test statistics for which the null hypothesis will reject?
The null hypothesis will not reject - it is a hypothesis and is not capable of rejecting anything. The critical region consists of the values of the test statistic where YOU will reject the null hypothesis in favour of the expressed alternative hypothesis.
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). --
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.
What is a Null Value and when are Null values used?
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.
Can composite key has null values?
if you want composite key for using the sql use the following sql query: select distinct(col_name) from table_name where col_name is null;
Are the first four descriptors in the x86 protected mode GDT null or is only the very first?
only the first descriptor is null , other can be assigned with different values.
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.
