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Wednesday, October 16, 2019

Data Science - Pandas- Series and Dataframe

Thsi Post have the complete syntax and code wise details of Pandas two Major concept Series and Data Frame.

Now Lets Start-





Thsi Post have the complete syntax and code wise details of Pandas two Major concept Series and Data Frame.
Now Lets Start-
# Pandas Series
#Series is a one-dimensional labeled array capable of
#holding data of any type (integer, string, float, python objects, etc.).
# The axis labels are collectively called index
In [1]:
1 import pandas as pd
2 import numpy as np
In [2]:
# A pandas Series can be created using the following constructor −
# pandas.Series( data, index, dtype, copy)
3 df = pd.Series()
4 df
Out[2]:
Series([], dtype: float64)
In [3]:
# A series can be created using various inputs like −
# Array
# Dict
# Scalar value or constant
In [4]:
# Create a Series from ndarray
    data = np.array(['D','I','Z','S','W','E','B'])
    s = pd.Series(data)
    s
Out[4]:
0 D 1 I 2 Z 3 S 4 W 5 E 6 B dtype: object
In [6]:
# Create a Series from ndarray
    data = np.array(['D','I','Z','S','W','E','B'])
    s = pd.Series(data, index =['001','002','003','004','005','006','007'])
    s
Out[6]:
    001 D 002 I 003 Z 004 S 005 W 006 E 007 B dtype: object
In [7]:
# Create a Series from dict
    data = {'D':1,'I':2,'Z':3,'S':4,'W':5.0,'E':6,'B':7.0}
    s = pd.Series(data)
    s
Out[7]:
D 1.0 I 2.0 Z 3.0 S 4.0 W 5.0 E 6.0 B 7.0 dtype: float64
In [8]:
# Create a Series from dict
    data = {'D':1,'I':2,'Z':3,'S':4,'W':5.0,'E':6,'B':7.0}
    s = pd.Series(data, index =['001','002','003','004','005','006','007'])
    s
# output will be NaN becuase in case of dictionary
# if the values not match with index it gices NaN
Out[8]:
001 NaN 002 NaN 003 NaN 004 NaN 005 NaN 006 NaN 007 NaN dtype: float64
In [9]:
# Create a Series from dict
    data = {'D':1,'I':2,'Z':3,'S':4,'W':5.0,'E':6,'B':7.0}
    s = pd.Series(data, index =['D','002','Z','004','W','006','B'])
    s
Out[9]:
    D 1.0 002 NaN Z 3.0 004 NaN W 5.0 006 NaN B 7.0 dtype: float64
In [12]:
# Create a Series from Scalar
    s = pd.Series(3, index = ['1','2','3','4','5','6'])
    s
Out[12]:
1 3 2 3 3 3 4 3 5 3 6 3 dtype: int64
In [13]:
# Create a Series from Scalar without index
    s = pd.Series(3)
    s
Out[13]:
0 3 dtype: int64
In [14]:
# Accessing Data from Series with Position
    s = pd.Series([1,2,3,4,5,6,7],index = ['D','I','Z','S','W','E','B'])
#retrieve the first three element
    print s[:3]
File "<ipython-input-14-fbdfbded2fb7>", line 2 s = pd.Series([1,2,3,4,5,,6,7],index = ['D','I','Z','S','W','E','B']) ^ SyntaxError: invalid syntax
In [16]:
# Accessing Data from Series with Position
    s = pd.Series([1,2,3,4,5,6,7],index = ['D','I','Z','S','W','E','B'])
# Retrieve the first three element
    print(s[:3])
    D 1 I 2 Z 3 dtype: int64
In [17]:
# Retrieve the last three elements.
    print(s[-3:])
    W 5 E 6 B 7 dtype: int64
In [18]:
# Retrieve Data Using Label (Index)
    print(s['D'])
In [19]:
# Retrieve multiple elements using a list of index label values.
    print(s[['D','Z','S','W']])
    D 1 Z 3 S 4 W 5 dtype: int64
In [20]:
# If a label is not contained, an exception is raised.
    print(s[['D','Z','S','W','Chauhan']])
    D 1.0 Z 3.0 S 4.0 W 5.0 Chauhan NaN dtype: float64
    c:\users\hp\appdata\local\programs\python\python37-32\lib\site-packages\pandas\core\series.py:1152: FutureWarning: Passing list-likes to .loc or [] with any missing label will raise KeyError in the future, you can use .reindex() as an alternative. See the documentation here: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#deprecate-loc-reindex-listlike return self.loc[key]
In [ ]:
# DataFrame
# Defination-A Data frame is a two-dimensional data structure,
# i.e., data is aligned in a tabular fashion in rows and columns ​
# Features of DataFrame
# Potentially columns are of different types
# Size – Mutable
# Labeled axes (rows and columns)
# Can Perform Arithmetic operations on rows and columns ​
# A pandas DataFrame can be created using the following constructor −
# pandas.DataFrame( data, index, columns, dtype, copy)

In [21]:
# How to create the Pandas DataFrame?
In [22]:
 ​
# Their are following methods to create the Pandas DataFrame.
# Lists
# dict
# Series
# Numpy ndarrays
# Another DataFrame
# Now lets us start the learning this with

In [23]:
    import pandas as pd
    import numpy as np​

# define the dataframe object
 ​    df = pd.DataFrame()​
# lets print this
    df
Out[23]:
In [24]:
    print(df)
Empty DataFrame Columns: [] Index: []
In [27]:
1 import pandas as pd
2 import numpy as np
3 ​
4 # define the dataframe object
5 data = [1,2,3,4,5,6,7]
6 df = pd.DataFrame(data)
7 ​
8 # lets print this
9 print(df)
0 0 1 1 2 2 3 3 4 4 5 5 6 6 7
In [28]:
1 df
Out[28]:
0
0 1
1 2
2 3
3 4
4 5
5 6
6 7
In [29]:
1 import pandas as pd
2 import numpy as np
3 ​
4 # define the dataframe object
5 data = [['Sawan',26],['Sandeep',25],['Shiv',24]]
6 df = pd.DataFrame(data,columns=['Name','Age'])
7 ​
8 # lets print this
9 print(df)
Name Age 0 Sawan 26 1 Sandeep 25 2 Shiv 24
In [31]:
1 import pandas as pd
2 import numpy as np
3 ​
4 # define the dataframe object
5 data = [['Sawan',26],['Sandeep',25],['Shiv',24]]
6 df = pd.DataFrame(data,columns=['Name','Age'], dtype=int)
7 ​
8 # lets print this
9 print(df)
Name Age 0 Sawan 26 1 Sandeep 25 2 Shiv 24
In [36]:
1 # Create a DataFrame from Dict of ndarrays / Lists
2 import pandas as pd
3 import numpy as np
4 ​
5 # define the dataframe object
6 data = {'Name':['Dizsweb','Sawan','Chauhan'] ,'Age' :[ 123, 26, 35]}
7 df = pd.DataFrame(data)
8 ​
9 # lets print this
10 print(df)
Name Age 0 Dizsweb 123 1 Sawan 26 2 Chauhan 35
In [37]:
1 # Create a DataFrame from Dict of ndarrays / Lists
2 import pandas as pd
3 import numpy as np
4 ​
5 # define the dataframe object
6 data = {'Name':['Dizsweb','Sawan','Chauhan'] ,'Age' :[ 123, 26, 35]}
7 df = pd.DataFrame(data, index =['R1','R2','R3'])
8 ​
9 # lets print this
10 print(df)
Name Age R1 Dizsweb 123 R2 Sawan 26 R3 Chauhan 35
In [39]:
1 # Create a DataFrame from List of Dicts
2 import pandas as pd
3 import numpy as np
4 data = [{'a':3,'b':4,'c':8},{'a':5,'d':6,'f':9},{'b':3,'c':8,'d':9}]
5 df = pd.DataFrame(data)
6 print(df)
a b c d f 0 3.0 4.0 8.0 NaN NaN 1 5.0 NaN NaN 6.0 9.0 2 NaN 3.0 8.0 9.0 NaN
In [44]:
1 # Creation of two Dataframe from the same data
2 import pandas as pd
3 data = [{'a': 1, 'b': 2},{'a': 5, 'b': 10, 'c': 20}]
4 ​
5 #With two column indices, values same as dictionary keys
6 df1 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b'])
7 ​
8 #With two column indices with one index with other name
9 df2 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b1'])
10 print(df1)
11 ​
12 print(df2)
a b first 1 2 second 5 10 a b1 first 1 NaN second 5 NaN
In [47]:
1 # Create a DataFrame from Dict of Series
2 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
3 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
4 ​
5 df = pd.DataFrame(d)
6 print(df)
7 ​
one two a 1.0 1 b 2.0 2 c 3.0 3 d NaN 4
In [48]:
1 # perticular column Selection
2 print(df['one'])
a 1.0 b 2.0 c 3.0 d NaN Name: one, dtype: float64
In [50]:
1 # Column Addition
2 import pandas as pd
3 ​
4 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
5 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
6 ​
7 df = pd.DataFrame(d)
8 ​
9 # Adding a new column to an existing DataFrame object with column label by passing new series
10 ​
11 print ("Adding a new column by passing as Series:")
12 df['three']=pd.Series([10,20,30],index=['a','b','c'])
13 print(df)
14 ​
15 print("Adding a new column using the existing columns in DataFrame:")
16 df['four']=df['one']+df['three']
17 ​
18 print(df)
Adding a new column by passing as Series: one two three a 1.0 1 10.0 b 2.0 2 20.0 c 3.0 3 30.0 d NaN 4 NaN Adding a new column using the existing columns in DataFrame: one two three four a 1.0 1 10.0 11.0 b 2.0 2 20.0 22.0 c 3.0 3 30.0 33.0 d NaN 4 NaN NaN
In [51]:
1 # Column Deletion
2 # Using the previous DataFrame, we will delete a column
3 # using del function
4 import pandas as pd
5 ​
6 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
7 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd']),
8 'three' : pd.Series([10,20,30], index=['a','b','c'])}
9 ​
10 df = pd.DataFrame(d)
11 print("Our dataframe is:")
12 print(df)
13 ​
14 # using del function
15 print("Deleting the first column using DEL function:")
16 del(df['one'])
17 print(df)
18 ​
19 # using pop function
20 print("Deleting another column using POP function:")
21 df.pop('two')
22 print(df)
Our dataframe is: one two three a 1.0 1 10.0 b 2.0 2 20.0 c 3.0 3 30.0 d NaN 4 NaN Deleting the first column using DEL function: two three a 1 10.0 b 2 20.0 c 3 30.0 d 4 NaN Deleting another column using POP function: three a 10.0 b 20.0 c 30.0 d NaN
In [55]:
1 # Row Selection, Addition, and Deletion with loc()
2 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
3 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
4 ​
5 df = pd.DataFrame(d, dtype=int)
6 print(df.loc['b'])
one 2.0 two 2.0 Name: b, dtype: float64
In [57]:
1 # Row Selection, Addition, and Deletion with iloc()
2 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
3 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
4 ​
5 df = pd.DataFrame(d, dtype=int)
6 print(df.iloc[2])
one 3.0 two 3.0 Name: c, dtype: float64
In [58]:
1 # Slice Rows
2 import pandas as pd
3 ​
4 d = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),
5 'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
6 ​
7 df = pd.DataFrame(d)
8 print(df[2:4])
one two c 3.0 3 d NaN 4
In [63]:
1 # Addition of Rows using append funtion
2 ​
3 import pandas as pd
4 ​
5 df = pd.DataFrame([[1, 2], [3, 4]], columns = ['a','b'])
6 df2 = pd.DataFrame([[5, 6], [7, 8]], columns = ['a','b'])
7 ​
8 df = df.append(df2)
9 print(df)
a b 0 1 2 1 3 4 0 5 6 1 7 8
In [64]:
1 # Deletion of Rows
2 ​
3 import pandas as pd
4 ​
5 df = pd.DataFrame([[1, 2], [3, 4]], columns = ['a','b'])
6 df2 = pd.DataFrame([[5, 6], [7, 8]], columns = ['a','b'])
7 ​
8 df = df.append(df2)
9 ​
10 # Drop rows with label 0
11 df = df.drop(0)
12 ​
13 print(df)
a b 1 3 4 1 7 8
In [65]:
1 # Python Pandas - Panel
2 # A panel is a 3D container of data.
3 # The term Panel data is derived from econometrics and
4 # is partially responsible for the name pandas − pan(el)-da(ta)-s.
5 ​
6 # The names for the 3 axes are intended to give
7 # some semantic meaning to describing operations
8 # involving panel data. They are −
9 ​
10 # items − axis 0, each item corresponds to a DataFrame contained inside.
11 # major_axis − axis 1, it is the index (rows) of each
of the DataFrames.
12
#     minor_axis − axis 2, it is the columns of each of the DataFrames.
13

14
# pandas.Panel()
15
# A Panel can be created using the following constructor −
16
# pandas.Panel(data, items, major_axis, minor_axis, dtype, copy)
17
# This class is removed from pandas now

Monday, October 14, 2019

Sql Server DBA Interview Question more than 1000

Question 1. What Is The Difference Between Lock, Block And Deadlock?


Solution -


Lock: DB engine locks the rows / page / table to access 
the data which is worked upon according to the query.
Block: When one process blocks the resources of another
process then the situation occured is called blocking. Blocking can be identified by using the following query
SELECT * FROM sys.dm_exec_requests 
where blocked <> 0
SELECT * FROM master..sysprocesses 
where blocked <> 0

Deadlock: When something happens as follows:
 Error 1205 is reported by SQL Server for deadlock.

Question 2. what is the sequence of SQL statement are processed in SQL Server?



Solution - The clauses of the select are processed in 

the following sequence
  1. FROM clause
  2. WHERE clause
  3. GROUP BY clause
  4. HAVING clause
  5. SELECT clause
  6. ORDER BY clause
  7. TOP clause

Question 3. on which TCP/IP port does SQL Server run?

Solution - By default SQL Server runs on port 1433. 
But according to requirement is can be changed such as we have more than one instance of SQL Server, 
Then  differenet port can be assigned to different Instances

Thursday, October 10, 2019

SQL Server constraint

CHECK constraint

A CHECK constraint can be applied to a column in a table to limit the values that can be placed in a column. Check constraint is to enforce integrity.

Sql Server Check Contraints Applicable query
After this if we used to insert the following query

insert into employees values(0,'Sawan','Chauan',24567)

Then following Output Message will be diplayed.
if SQL Constraints fails then following output will be displayed

Second Example of Query

SQL Server Check Constraints

When we try to insert the following -
Check Contraints complete query SQL server 2017
Then we will receive the above error



TRY----CATCH constructs

To handles exceptions by writing scripts inside the TRY block and error handling in the CATCH block

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