Expert's Guidance

  Updating Dictionary You can update a dictionary by adding a new entry or a key-value pair, modifying an existing entry, or deleting an existing entry as shown below in the simple example − When the above code is executed, it produces the following result − dict['Age'] : 8 dict['School'] : DPS School Delete Dictionary Elements You can either remove individual dictionary elements or clear the entire contents of a dictionary. You can also delete the entire dictionary in a single operation.  To explicitly remove an entire dictionary, just use the del statement. Following is a  simple example − Accessing Values in Tuples To access values in a tuple, use the square brackets for slicing along with the index or indices to obtain the value available at that index. For example − When the above code is executed, it produces the following result − tup1[0] : physics tup2[1:5] : [2, 3, 4, 5] Updating Tuples Tuples are immutable which means you cannot update or change the values of ...

Python includes following list methods  1) list.append(obj) = Appends object obj to list  2) list.count(obj) = Returns count of how many times obj occurs in list  3) list.extend(seq) = Appends the contents of seq to list 4) list.index(obj) = Returns the lowest index in list that obj appears 5) list.insert(index, obj) = Inserts object obj into list at offset index 6) list.pop(obj=list[-1]) = Removes and returns last object or obj from list 7) list.remove(obj) = Removes object obj from list 8) list.reverse() = Reverses objects of list in place 9) list.sort([func]) = Sorts objects of list, use compare func if given Function with Description 1) cmp(tuple1, tuple2) = Compares elements of both tuples. 2) len(tuple) = Gives the total length of the tuple. 3) max(tuple) = Returns item from the tuple with max value. 4) min(tuple) = Returns item from the tuple with min value. 5) tuple(seq) = Converts a list into tuple. Built-in Dictionary Functions & Methods Python includes ...

  Difference between Super Key and  Candidate Key Last Updated: 23-02-2021 Super Key: Super Key is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation. All super keys can’t be candidate keys  but its reverse is true. In relation, the number of super keys is more than the  number of candidate keys. Example: We have a given relation R(A, B, C, D, E, F) and we shall check for being  super keys by following given dependencies: Functional  dependencies                Super key AB->CDEF                                      YES CD->ABEF                                      YES CB->DF                            ...

 Last Updated: 23-02-2021 Primary Key: A primary key is used to ensure data in the specific column is unique. It is a column that cannot have NULL values. It is either an existing table column or a column that is specifically generated by the database according to a defined sequence. Example: Refer to the figure – STUD_NO, as well as STUD_PHONE both, are candidate keys for relation STUDENT but STUD_NO can be chosen as the primary key (only one out of many candidate keys). Foreign Key: A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It is a column (or columns) that references a column (most often the primary key) of another table. Example: Refer to the figure – STUD_NO in STUDENT_COURSE is a foreign key to STUD_NO in STUDENT relation. Figure: Let’s see the difference between Primary Key and Foreign Key: PRIMARY KEY A primary key is used to ensure data in the specific column is unique. It uniquely identifie...