UNION Operation.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Microsoft Access Runtime. Select Language:. Choose the download you want. Download Summary:. Total Size: 0. Back Next. Microsoft recommends you install a download manager. Microsoft Download Manager. If the queries to union are very different, you might encounter a situation where an output field must combine data of different data types. If so, the union query most often will return the results as a text data type since that data type can hold both text and numbers.

To understand how this works, we’ll use the Product Transactions union query in the Northwind sample database. Open that sample database and then open the Product Transactions query in datasheet view. The last ten records should be similar to this output:. Let’s assume you want the Quantity field split into two – Buy and Sell. Let’s also assume you want to have a fixed zero value for the field with no value. Here’s how the SQL will look for this union query:.

If you switch to datasheet view, you’ll see the last ten records now displayed like the following:. Continuing this example, what if you want the fields with zero to be empty?

You can modify the SQL to display nothing instead of zero by adding in the Null keyword like the following:. However, as you might have observed switching to datasheet view, you now have an unexpected result. In the Buy column, every field is cleared:. The reason this happens is because Access determines the data types of the fields from the first query. In this example, Null is not a number.

So what happens if you try and insert an empty string for the blank value of fields? The SQL for this attempt might look like the following:. When you switch to datasheet view, you’ll see that Access retrieves the Buy values, but it converted the values to text. You can tell these are text values since they are left-aligned in the datasheet view. The empty string in the first query is not a number which is why you see these results. You’ll also notice that the Sell values are also converted to text because the purchase records contain an empty string.

A solution is to force the query to expect the field value to be a number. That can be accomplished with the expression:. The condition to check, False , will never be True , thus the expression will always return Null , but Access still evaluates both output options and decides the output to be numeric or Null. An alternative method to achieve the same result is to prepend the queries in the union query with yet another query:.

For each field, Access returns fixed values of the data type you define. Of course, you don’t want the output of this query to interfere with the results so the trick to avoid that is to include a WHERE clause to False:. This is a little trick since this is always false and then the query doesn’t return anything. Combining this statement with the existing SQL and we arrive at a completed statement as follows:. The reason for this discrepancy is because two records are not unique.

A special case for a union query is to combine a set of records with one record that contains the sum of one or more fields. Here is another example that you can create in the Northwind sample database to illustrate how to get a total in a union query. Combine these two queries into a union query to append the record with the total quantity to the purchase records:. Switch to datasheet view and you should see the four purchases with the sum of each followed by a record that totals the quantity:.

That covers the basics of adding totals into a union query. You can review using fixed values in the section Combine three or more tables or queries in a union query. Union queries in Access by default only include distinct records.

But what if you want to include all records? Another example might be useful here. In the previous section, we showed you how to create a total in a union query. The reason you see this result is because on one day the same quantity of chocolates was sold twice – as recorded in the Purchase Order Details table.

Here’s a simple select query result showing both records in the Northwind sample database:. This will mostly likely have an impact on the sorting of the results, so you might want to also include an ORDER BY clause to determine a sort order. Here’s the modified SQL building off the previous example:. Switch to datasheet view and you should see all the details in addition to a total as the last record:.

A common usage for a union query is to serve as the record source for a combo box control on a form. You can use that combo box to select a value to filter the form’s records. For example, filtering the employee records by their city. To see how this might work, here’s another example that you can create in the Northwind sample database to illustrate this scenario. Looking at those results you might not see a lot of value.

Expand the query though and transform it to a union query by using the following SQL:. Now that you have a completed union query displaying each city name only once, along with an option that effectively selects all cities, you can use this query as the record source for a combo box on a form.

Using this specific example as a model, you could create a combo box control on a form, set this query as its record source, set the Column Width property of the Filter column to 0 zero to hide it visually, and then set the Bound Column property to 1 to indicate the index of the second column. In the Filter property of the form itself, you can then add in code such as the following to activate a form filter using the value of what was selected in the combo box control:.

Advanced queries. Use a union query to combine multiple queries into a single result. Company, Customers. Company, Suppliers. Company, Employees. That can be accomplished with the expression: IIf False, 0, Null The condition to check, False , will never be True , thus the expression will always return Null , but Access still evaluates both output options and decides the output to be numeric or Null. Of course, you don’t want the output of this query to interfere with the results so the trick to avoid that is to include a WHERE clause to False: WHERE False This is a little trick since this is always false and then the query doesn’t return anything.

Use a union query to filter records on a form through a combo box control. City, Employees. In the Filter property of the form itself, you can then add in code such as the following to activate a form filter using the value of what was selected in the combo box control: Me. Top of Page. A subscription to make the most of your time. Try one month free. Need more help?

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Microsoft access 2016 union query free download. Create a query based on multiple tables

 
The UNION operation in Access creates a union query, which combines the results of two or more independent queries or tables. I’m using Office I have an Access Database that I’ve worked on for the past couple weeks, and I finally have a query that reports what.

 
 

Use a union query to combine multiple queries into a single result – Microsoft Support

 
 

The question becomes whether or not to use the ALL syntax. Use Authors table in SQL Server Pubs database or just use microsoft access 2016 union query free download simple table with these values obviously по этой ссылке to just illustrate the point :.

This SQL statement combines two queries to retrieve records based on states. The two queries happen to both get records from Tennessee ‘TN’ :. Notice how this displays the two query results in the order they appear from the queries. The example above is very simple for illustrative purposes, and can obviously /29402.txt done without using a UNION query.

Each of query could reference completely different sets of tables. For instance, you can combine the list of узнать больше codes with customers who purchased a particular product recently with zip codes that have total sales exceeding a certain amount.

The fields don’t have to come from the same table, or even same field names since you can use the AS syntax to give the field a different name from its source. This is commonly used as the rowsource of combo boxes to give people a choice of None “”. For example:. To do this in SQL Server, it must build a temporary index on all the columns returned by both queries. If the index cannot be built for the queries, a Читать статью error occurs.

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