Basic UNIX commands

How to create a new file ?

syntax : cat>filename
file data
file data
fild data

CTTL+D

How to rename existing file name ?

Syntax : mv oldfilename >> newfilename

How to change existing file content ?

Syntax: vi filename 

do all changes, if you want to save the file type the below command

:wq!

How to see the content of file ?

Syntax : cat <file name >

How to identify duplicate records in file ?(any file like DAT,CSV,TXT)

Syntex: cat <file name> | uniq -d

How to fetch unique records in file ?(any file like DAT,CSV,TXT)

Syntex: cat <file name> | uniq 

What is the difference between union and union all ?    

Let us assume, i have two tables 

Table 1

Table 2 

Table 1 have the following records

1

2

3

4

5

Table 2 have the following records

5

6

7

8

9

10

Now fire the below query in SQL Assistant

Select * from table1 

Union

Select * from table2

Now we will get below records..

1

2

3

4

5

6

7

8

9

10

So we come to know, when ever we use union key word, it fetches only unique records.

Select * from table1

Union all

Select * from table 2

We well get the below records 

1

2

3

4

5

5

6

7

8

9

10

If you use union all keyword between two or more SQL statements, we will get the unique records as well as duplicates will fetches.

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