Union

Union can help you combine two similarly structured tables vertically. That is, it is to append a table below another table, so it adds more rows to the original table. Generally, Union is used for two tables with the same or similar properties of columns.

Union is to append a table below another table

Inputs

The Union action requires two pieces of inputs:

• Table names that you want to append together

• Columns names that allow the exact one to one mapping of each column from one table to the other

Acho will automatically recognize column names that are exactly matching from the two tables and assume that those are to be stacked together. However, if the naming convention from the two sides differs, some effort will need to be spent on specifying the mapping.

Union multiple tables

You can feel free to append more than two tables at the same time. By clicking the icon , you can add one more table to merge together. You can also remove the table by clicking the icon .

If you have multiple CSV files with exactly the same number of columns and column names, you can also try uploading them as Multiple CSV files. This method combines multiple CSV files as a single resource by using Union.

Modify the number of columns to map

If you don't want to append tables based on all columns, you can click the minus icon to remove the columns that you don't need. If you remove some of the columns accidentally, you can click the plus icon to get those columns back.

The maximum number of columns cannot exceed the number of columns in the first table. Take the above graph as an example. If the orders_Jan table has 3 columns, the maximum number of the columns that you can specify is 3 even if the order_Feb table has 4 columns.

Union Example

Below is a demo table called "customers" :

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfred Futterkiste	Maria Anders	43 53rd Ave	New York	12209	USA
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico

and another demo table called "suppliers":

SupplierID	SupplierName	ContactName	Address	City	PostalCode	Country
1	Exotic Liquid	Charlotte Cooper	49 Gilbert St.	London	EC1 4SD	UK
2	New Orleans Cajun Delights	Shelley Burke	P.O. Box 78934	New Orleans	70117	USA
3	Grandma Kelly's Homestead	Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA

By applying the Union action, you would need to provide the column mapping between these two tables. Also, make sure that all column types match well. For example, a string column can only be merged with a String column.

Below is the result table after Union. As indicated, ContactName, Address, City, PostalCode, and Country are now merged.

ContactName	Address	City	PostalCode	Country
Maria Anders	43 53rd Ave	New York	12209	USA
Charlotte Cooper	49 Gilbert St.	London	EC1 4SD	UK
Regina Murphy	707 Oxford Rd.	Ann Arbor	48104	USA
Shelley Burke	P.O. Box 78934	New Orleans	70117	USA
Ana Trujillo	Avda. de la Constitución 2222	México D.F.	5021	Mexico
Antonio Moreno	Mataderos 2312	México D.F.	5023	Mexico

Troubleshooting

• Why some of the rows are duplicated?

The Union action uses UNION ALL function in SQL. It appends all data points from one dataset to another dateset no matter whether some rows are duplicated. If you don't want to have duplicated records, you can use the deduplicate function to filter out redundant rows.