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Articles by Lakshmi Srinivas
Page 17 of 24
How can we delete multiple rows from a MySQL table?
We can use DELETE statement along with a WHERE clause, which identifies those multiple rows, to delete multiple rows from MySQL table.Examplemysql> Select * from names; +------+-----------+ | id | name | +------+-----------+ | 1 | Rahul | | 2 | Gaurav | | 3 | Raman | | 5 | Ram | +------+-----------+ 4 rows in set (0.00 sec) mysql> DELETE from names WHERE id > 2; Query OK, 2 rows affected (0.04 sec)The query above will delete multiple rows because WHERE clause identify two rows having id > 2 from table ‘names’.mysql> Select * from names; +------+-----------+ | id | name | +------+-----------+ | 1 | Rahul | | 2 | Gaurav | +------+-----------+ 2 rows in set (0.00 sec)
Read MoreWhat are the different ways to maintain data integrity in child table when the record is deleted in parent table?
When two tables are connected with Foreign key and data in the parent table is deleted, for which record exists in child table too, then followings are the ways to maintain data integrity −On Delete CascadeThis option will remove the record from child table too if that value of the foreign key is deleted from the main table.On Delete Null This option will set all the values in that record of child table as NULL, for which the value of the foreign key is deleted from the main table.
Read MoreHow can we remove NOT NULL constraint from a column of an existing MySQL table?
We can remove a NOT NULL constraint from a column of an existing table by using the ALTER TABLE statement.ExampleSuppose we have a table ‘test123’ having a NOT NULL constraint on column ‘ID’ as follows −mysql> DESCRIBE test123; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | ID | int(11) | NO | | NULL | | | Date | date | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.04 sec)Now if we ...
Read MoreHow to Calculate the Area of a Triangle using Python?
Calculating the area of a triangle is a formula that you can easily implement in python. If you have the base and height of the triangle, you can use the following code to get the area of the triangle,def get_area(base, height): return 0.5 * base * height print(get_area(10, 15))This will give the output:75If you have the sides of the triangle, you can use herons formula to get the area. For example,def get_area(a, b, c): s = (a+b+c)/2 return (s*(s-a)*(s-b)*(s-c)) ** 0.5 print(get_area(10, 15, 10))This will give the output:49.607837082461074
Read MoreHow do I run two python loops concurrently?
You will need to use a multiprocessing library. You will need to spawn a new process and provide the code to it as an argument. For example,from multiprocessing import Processdef loop_a(): for i in range(5): print("a") def loop_b(): for i in range(5): print("b") Process(target=loop_a).start() Process(target=loop_b).start()This might process different outputs at different times. This is because we don't know which print will be executed when.
Read MoreHow to write inline if statement for print in Python?
Python provides two ways to write inline if statements. These are:1. if condition: statement2. s1 if condition else s2Note that second type of if cannot be used without an else. Now you can use these inline in a print statement as well. For example,a = True if a: print("Hello")This will give the output:Helloa = False print("True" if a else "False")This will give the output:False
Read MoreWhat is the associativity of Python's ** operator?
From the Python docs:Operators in the same box group left to right (except for comparisons), including tests, which all have the same precedence and chain from left to right — see section Comparisons — and exponentiation, which groups from right to left).So the ** operator(exponentiation) is right to left associative. For example,2 ** 3 ** 4 will be evaluated as: (2 ** (3 ** 4))For example,print(2 ** 3 ** 0)This will give the output:2
Read MoreHow to put comments inside a Python dictionary?
You can put comments like you normally would anywhere in a python script. But note that you can only put single line comments using #. Multiline comments act like strings and you cannot put just a string in between definition of a dict. For example, the following declaration is perfectly valid:testItems = { 'TestOne': 'Hello', # 'TestTwo': None, }But the following is not:testItems = { 'TestOne': 'Hello', """ Some random multiline comment """ }
Read MoreHow to sort a Python dictionary by datatype?
You can sort a list of dictionaries by values of the dictionary using the sorted function and passing it a lambda that tells which key to use for sorting. For example, A = [{'name':'john', 'age':45}, {'name':'andi', 'age':23}, {'name':'john', 'age':22}, {'name':'paul', 'age':35}, {'name':'john', 'age':21}] new_A = sorted(A, key=lambda x: x['age']) print(new_A)This will give the output:[{'name': 'john', 'age': 21}, {'name': 'john', 'age': 22}, {'name': 'andi', 'age': 23}, {'name': 'paul', 'age': 35}, {'name': 'john', 'age': 45}]You can also sort it in place using the sort function instead of the sorted function. For example, A ...
Read MoreJava program to find the permutation when the values n and r are given
Permutation refers a number of ways in which set members can be arranged or ordered in some fashion. The formula of permutation of arranging k elements out of n elements is −nPk = n! / (n - k)!Algorithm1. Define values for n and r. 2. Calculate factorial of n and (n-r). 3. Divide factorial(n) by factorial(n-r). 4. Display result as a permutation.Exampleimport java.util.Scanner; public class Permutation { static int factorial(int n) { int f; for(f = 1; n > 1; n--){ ...
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