Why this uses two different aliases for the same table?

1

Hello

Regarding the statement below, can you explain why would it be needed to use two aliases for the same table?

FROM [Table1] p
LEFT JOIN [Table2] c on c.[Col1] = p.Col2
LEFT JOIN [Table2] cc on cc.[Col1] = p.Col3

Thanks!

2

Sounds like homework. Please researxh the word alias

3

My point is why not do:

FROM [Table1] p
LEFT JOIN [Table2] c on c.[Col1] = p.Col2
LEFT JOIN c on c.[Col1] = p.Col3

4

Because you cant in ms sql

5

Oh I see. So, in the resulting table, will c.[Col2] be different to cc.[Col2]? Or they will be exactly the same and they can be used interchangeably?

6

hi

the way to do this is

FROM [Table1] p
LEFT JOIN [Table2] c on c.[Col1] = p.Col2
LEFT JOIN c on c.[Col1] = p.Col3


FROM [Table1] p
LEFT JOIN [Table2] c on c.[Col1] = p.Col2 OR  on c.[Col1] = p.Col3
7

Thanks!
Will they produce the same results of the first will potentially produce duplicates while the second won't?

8

We can do some TESTING with sample data to find out

mind you .. there is a type of mental fallacy .. the test results will be what you expect BUT not for the reasons
you think ..so in other scenarios MAY give error

9

These scenarios are what I am worried about, can you elaborate when it will give errors?
Thanks!

10

One Scenario .. name is not an exact match

image
image623×735 8.86 KB

please google search for SQL Data Anamolies

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