Merge & Append Queries

The ability to combine queries is powerful because it allows you to append or merge different tables or queries together.

Why we need to Merge / Append queries?

You can combine tables into a single table in the following circumstances:

• Too many tables exist, making it difficult to navigate an overly-complicated data model. You combine the tables together to make it ease of working. It helps to reduce time in ETL process.
• Several tables have a similar role, for example. You have set a tables depicting sales every month. You can simple append the tables for further analysis.
• A table has only a column or two that can fit into a different table.
• You want to use several columns from different tables, simple join the tables using Merge query.

Append queries:

• When you append queries, you will be adding rows of data from one table to another table or query. 
• For example, you could have two tables, one with 300 rows and another with 100 rows, and when you append queries, you will end up with 400 rows.
• The pertinent columns that you require in your combined table must be named the same in your original data tables to see one consolidated view. In other words, the columns should be same in both the tables.

Merge Queries:

When you merge queries, you will be adding columns from one table (or query) into another. 

To merge two tables, you must have a atleast one common column that is the key between the two tables.

• This process is similar to the JOIN clause in SQL. A JOIN is used to combine rows from two or more tables, based on a related column between them
• When you merge queries, you are combining the data from multiple tables into one based on a column that is common between the tables. 
• You can merge two queries or tables in different ways so that you can view your data in the most appropriate way for your business requirements.

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