MIS 610 Grand Canyon University Communication & Networking Discussion

I need support with this Writing question so I can learn better.

respond to 3 discussions.

1.

The Union function is essentially a way to combine different metadata tables’ results together into one for usage in data manipulation. This can become very useful if the user needs to combine tables that may not necessarily fit the join criteria but we may still want to see everything in one place.

Unions join SELECT statements as shown:

SELECT Name

From Example_A

Union

SELECT Customer

From Example_B

The resultant table will be a combination of Name and Customer from their respective tables, but results will be placed on one single, common column. The result column will take the tag of the first select statement, but you can change the name by using an AS statement in the first SELECT statement.

This is an incredible resource, but it can be a bit messy. The meshing of data like this can lead to confusion is not properly labeled and documented. One way to help in understanding is to bring in common columns between the UNIONS to help give expression and detail to the results. It goes without saying that the use of a UNION is not to replace the JOIN. There should be a consensus on why the UNION is happing, like joining all money spent, all vendors. This type of join is easier to explain and thus the results are less confused.

2.

The UNION operator combines the results of two or more queries into a distinct single result set that includes all the rows that belong to all queries in the UNION. In this operation, it combines two more queries and removes the duplicates. There are some pre-conditions that need to be followed by the select statements whenever using the UNION function else it might result in an exercise in futility, these include that fact that; statements should have same order, the SELECT statements in the UNION should have same data type, and they should have same columns selected.

Example:

SELECT [name], age

FROM Person.Person

WHERE age < 45

UNION

SELECT [name]

FROM Person.Employee

WHERE [name] LIKE ‘%es%’

One weakness of the UNION is that it verifies if there are duplicate values and removes them from the query results, and this aspect can slow down a query. Now to improve UNION function we can use the UNIONALL function. In this the resultant table will consist of all the elements from both the tables which makes it easy to sort this table and remove duplicates from it. In the same vein, we can also use the WHERE condition directly into the SELECT statements so this will result in fast sorting of the data and remove duplicates from it.

3.

Union means joining two or more data sets into a single set. In SQL Server, Union is used to combine two queries into a single result set using the select statements. Union extracts all the rows that are described in the query.

Syntax –

query1 UNION query2

Union holds a few conditions before being used in a query. One such condition is that the rows to be extracted must come from the same columns from the tables.

Example –

select name, rollnumber

from student

UNION

select name, rollnumber

from marks

A union is used for extracting rows using the conditions specified in the query while Union All is used for extracting all the rows from a set of two tables.

Syntax –

query1 UNION ALL query2

The same conditions are applicable to Union All. The only difference between Union and Union All is that Union extracts the rows that are being specified in the query while Union All extracts all the rows including the duplicates (repeated values) from both the queries.

https://www.geeksforgeeks.org/union-and-union-all-…

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