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Introduction to queries (Access basics, part 3)
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Now that weve built tables and relationships, its time to design
and build some queries,and these are another essential piece of any
database.Queries are literally questions you ask of your data,and
in fact, asking the question you want answered can be a good place
to start.For example, How many orders did Tailspin Toys place last
month?That language in that question points you to the Orders
table,and from there, you select the fields you want to see, build
the query, and then run it.And thats the basic process or flow for
most queries.You ask your question, and then you pick a data
sourcethe tables or queries with the data that will answer that
question.From there, you pick the fields you want to see in the
result (which is also called a dataset, by the way),and add any
criteria.In this example, the criteria filter the results to
Tailspin Toys for the month of May,but criteria can do a lot more
than that, and well look at them in the next video.And you can use
queries for more than just answering questions.Theyre like a
multi-tool or combination pliers; they can be one of the handiest
tools in any database.For example, they can provide the data for
forms and reports, and they can also make bulk changes to your
data.Now, you can build several types of queries in any database,
and to show you what you can do in Access,Ill select Create, then
Query Design.Ill close the Show Table dialog because I want you to
see these commands. These are the types of queries you can
create.Youve already seen me build a Select query. Theyre the most
common, and theyre how you get answers out of your data.A Make
Table query lets you select records from an existing table and save
them as a new table.That can be handy, say, if you import a big
Excel file and you want to break some of that data into separate
tables.Now, you run these next 3 queries against existing
data.Append queries add data to existing tables, Update queries
change existing data,and Delete queries do just that, they delete
data.You use a Crosstab query when you need to display summary data
such as averages or sums.For example, if you need to see sales by
region, you use a Crosstab query.Heres what one looks like in the
query designer, and the results look like this.You can see this one
returns sales data per quarter.A Union query lets you combine
multiple Select queries into a single result,and this is something
you do when you need to see data from unrelated sources.Pass
Through queries let you connect to a large database,such as
Microsoft SQL Server, and process queries on that database.When you
do that, Access becomes a front end, a set of tools that helps you
run the larger database.And finally, Data Definition queries let
you create or modify tables and indexes.The thing is, Access
provides so many other ways to create tables and change
indexes,youll probably never use this type of query.So for the rest
of this course, Im going to concentrate on Select queries, because
theyre the ones youll use the most.And to build one, Ill go to the
Create tab and select the Query Wizard.If youre new to queries,
this is a nice place to start. Choose Simple Query Wizard, and the
Phone Numbers table.Ill select the Customer and Phone Number
fields, choose Next,change the name if I want to, display the
results, and select Finish.Theres the result, but you probably have
a couple questions.For example, what kind of query did you just
create,and how do you know whether youre calling someones office
phone or their fax machine?You can answer those questions by adding
some data to the query,and to do that, select Home, then View, then
Design View. This starts the Query Designer.The designer shows you
the data sourcein this case its a table,but it can also be a
queryand the fields involved in the query.The ribbon will always
tell you the type of query, and in this case you can see its a
Select query.To add the Type field and make the phone list easier
to use, you just drag and drop,and to see the results, you select
Run here on the Design tab.Now, you can only do so much with the
Query Wizard.For example, it doesnt let you add formulas, so for
the rest of this course Ill use the designer.And next, Ill show you
how to build a select query from scratch with the designer,and how
to add some basic criteria to help you answer your questions.
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In this video, Ill use the Query Designer to create a Select
query from scratch,and well follow the process I described in the
previous video.Ill select a data source, fields from that data
source, and as needed, well add criteria to filter the results.As a
demo, lets answer the question from the previous video: How many
orders did Tailspin Toys place last month?On the ribbon, choose
Create, then Query Design. That starts the designer.You can use the
Show Table dialog to add tables or queries as a data source,or you
can just drag a source over from the Navigation pane.For this
example thats the Orders table, and to answer our question, we need
customer names and order dates.You can double-click to add a field
to the design grid down here, or you can drag and drop.So if I run
the query now, you can see it returns every order for every
customer,and I can use the filtering tools here to narrow the
results.But, if you add criteria to the query, you can get the same
result every time.Thing is, adding criteria gets a little more
complicated, so you need to remember a couple rules.And the first
rule is: You need to know your data.To show you what I mean, Ill
open the Orders table, select Fields on the ribbon, then the fields
in our query.You can see Order Date is a Date/Time field, but
Customers isnt a Text field, its a Number field.And that leads to
the second rule: Your criteria has to match the data type of the
field youre filtering.For instance, you can only enter date values
in a Date/Time field, numbers in a Number field, and so on.So how
do I know which number corresponds to Tailspin Toys?Ill start by
going to Database Tools, Relationships,and I see Customers and
Orders are related by the ID and Customer ID fields.So I open the
Customers table, locate Tailspin Toys, and I see it has an ID value
of 23.So back to the query, and Ill enter 23 in the Criteria row of
the Customer ID field.Then Ill expand the Order date field,and add
a pair of logical operators, BETWEEN and AND, and Ill put a
starting date here, and an ending date here.And notice I surround
the date values with pound signs.Access requires those because they
identify the value as a date, and not text.So run the query and
there you go. Just the orders placed by Tailspin last month.Now
lets look at the query designer for a minute. Do you see these
check boxes?If you clear them, you hide your field from the result,
like so.The field is still in the query, you just dont see it in
the results.Also, if you want to return a portion of the
result,such as the top 5 values or maybe the bottom 25 percent of a
data set, select a value from the Return list.Then here in the
design grid, go to the Sort row and select Ascending or
Descending.Ascending order returns the bottom items, and Descending
returns the top items.So next, look at the Totals button?This is a
fast way to add sums, averages and other calculations to a query,
and here's an example.You can see we have three tables and a field
from each,and if I run the query as it is now, we get a lot of
repeated categories.So back to design view, click Totals, and
notice that Access groups all the records in the query.Run the
query again, and now it calculates the number of items sold in each
category.Sort the results, and you can see which categories sell
the most or the least.So next, Ill show you how to create a Select
query that uses multiple data sources.That involves understanding a
database component called a join, so keep going.
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Building a select query that uses more than one data source
follows the same basic stepsas a query with a single data
source.You start the query designer, select your tables or queries,
and add your fields.But, theres a twist here: When you query
multiple sources for data, you need to create a match between each
source.For example, if you want to know which products are in a set
of orders, you have to match the orders with their products.To
create those matches, you use whats called a join.A join compares
the data in two common fieldsone from each data sourceand it
controls how the data in each field is matched.For example, the
most common type of join only returns data from one field when it
finds a matching value in the other and this is how you find out
the number of products in each order, for example.And another type
of join returns all the data from one field, but only matching data
from the other.And in this example, the querys telling you which
orders dont contain a given product.Now, when you created your
table relationships, Access also created a join for each
relationship.Access uses your relationships as patterns for
joins,so most of the time, your joined fields will be your primary
and foreign keys.But they dont have to be. You can join unrelated
sources, and Ill show you how later in this course.But if you do
have two related sources, and you add them to the Query designer,
you see what looks like the relationship.Just remember that it
isnt.Access is just telling you the type of relationship it used as
the pattern for the join.And, as long as you have a join between
your tables or queries, you can add fields from both sources.And
notice, too, that I didnt add the joined fields to the design
grid.You dont need to, because Access adds them behind the
scenes.You can run the query and get a result.So lets go back and
look at joins some more, because you need to remember a few
facts.First, you can set or change the type of join by
right-clickingor double-tapping the join line and selecting Join
Properties.That starts the Join Properties dialog, and these
settings control the type of join in your query,and these are three
most common types of joins.This option creates an inner join.This
is the type of join that returns matching data from both tables,and
Access creates this type of join whenever you create a
relationship.The second option creates a left outer join,which
means that your query returns all the data from the table listed on
the left,and only matching data from the other table.The third
option creates a right outer join, and you can probably guess what
happens.The query returns all the data from right-hand table, and
only matches from the left.You typically use outer joins when you
want to know what hasnt sold,or (more generically) when something
hasnt happened.Now, I said earlier that these are the three most
common types of joins.You can also use cross joins and unequal
joins, but you wont use them very often, so I wont cover them
here.If you want to know more, see the links in the Course
Summary.And in addition to the types of joins, you also need to
remember that relationships and joins arent the same thing.A
relationship is a set of rules that controls referential integrity,
how you add and delete data.Joins control how your query matches
data.But the two can be kind of similar. For example, your
relationships can have sides, one and many,and, your joins can also
have sides, left and right.But, you only use joins in queries, and
you can use them in ways that you cant in relationships.For
example, you can delete joins without harming your database,
something you cant do with a relationship.Also, you can add joins
where relationships dont exist.As an example, you can join a field
in a table with a field in a query as long as those fields have a
matchingor compatible data types, and Ill show you how to do that
later in this course.But first, we need to take another look at
outer joins, so keep going.
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Let's look at how to use left and right outer joins in a Select
query.And as a quick review, outer joins have sides, left and
right,and they return all the data from one table, and only
matching data from the other.So now lets add just a little bit to
this.The table that returns all data is called the base table,and
the table that returns matches is called the secondary table.Also,
the base and secondary tables vary, depending on the direction of
the join.If you use a right outer join, the right-side table
becomes the base table, and so on.And remember, you control left
and right by selecting and then either right-clicking or
double-tapping the join line,then Join Properties, then choosing
the second or third options.So let's put this to work. Create tab,
Query Design, and I'll add the Order Details and Products
tables.You can see Access used a one-to-many relationship as the
pattern for the join, and that means it's an inner join.I'll add
the Product Name and Quantity fields, and if I run the query,you
can see it only returns data for products that have been ordered.I
know this because If the query was returning data for unordered
products, wed see blank records here.So back to Design view,
right-click or double-tap the join line and start the Join
Properties dialog.Select the second option, and notice the join
line.The arrow tells you it's an outer join, and it also points to
the secondary table.Run the query, sort the data from smallest to
largest, and now you know which products don't sell.So what happens
if you change to a right outer join?I'll make the change, run the
query, and we get the same results as an inner join, no blank
records.If we look at the Join Properties dialog, we see why.We're
returning all the data from the Order Details table, but only
matches from the Products table.In other words, we're only seeing
products that have a corresponding order,and that's the same result
returned by an inner join.So think your joins through, and if you
dont get the result you want, you can always change them.And next,
I'll show you how to add joins and how to use indirect joins,and
those are two ways to query unrelated tables and get some logical
results.
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At times, you'll need to query tables or other data sources that
arent related, that dont share a join,and you have two options for
doing that.You can use an intermediate table, a table that shares
joins with the data sources you want to use,or, if you dont have
any intermediate tables, you can add joins.So I'll start with the
intermediate table, and as an example, in this database,employees
have to enter a status for each order, but sometimes they
forget.The question you want to answer, then, is which orders dont
have a status, and which employees forgot to enter them?On the
surface, it looks like we need to use three tables in the
queryEmployees, Orders, and Order Details Statusbecause they
correspond to the data points in our question:Which orders dont
have a status, and which employees forgot to enter the status?So
add them to the query, and you can see these two tables arent
joined, but thats okay, right? I can add joins.So Ill join on the
ID fields, run the query, and nothing.So now Ill do what I should
have done in the first place and look at the relationships between
the tables.When I do, you can see what looks like a chain of
relationships hereEmployees to Orders,Orders to Order Details, and
Order Details to Order Details Status.So Orders and Order Details
Status arent related, but Order Details is related to them
both.That makes Order Details my intermediate table.And in turn,
that leads to a rule: As long as the intermediate tables are part
of your data source,you can query these unrelated tables and get a
valid result.You dont have to include the intermediate table in
your results, but it has to be part of your querys data source.So
Ill add the OrderDetails to the query, keep the fields the same,
and run the query.Filter for blank values, and theres your
answer.Now lets add a join to a query, and to do this, you need to
keep some rules in mind:First, the tables or queries you want to
join need to have fields with matching or compatible data types.And
as an example of that, the Number and Currency data types are
compatible, but Number and Text arent.Second, the join you create
only resides in your query. Youre not creating a table relationship
here.Third, the results should make sense.If the join returns data
on orders and company cars, for example, you should probably start
over.So as an example, lets say we need to know which customers
ordered which products.Ill add Customers, Orders, and Order Details
to a new query.Now Ill add the join. Ill drag Customer ID from
Customers here to the matching field in the Orders table.Theres the
join line, and heres another rule: Access places the field you drag
on the left side of the new join.If that isnt what you want, select
the join line, press Delete, and start over.Now that we got that
taken care of, we can build the query.Ill add FirstName and
LastName from Customers, then ProductID, OrderID, Quantity, and
UnitPrice from OrderDetails.Run the query, and theres your data.If
you're wondering, it would have been easier, and more logical,to
create a table relationship between the Customers and Orders
tables.If you don't remember how to do that, see the second course
in this series,Creating relationships between your tables.And from
here, you continue building your database by creating forms and
reports.Forms can make data entry easier, faster, and a lot more
accurate,and they also give your database a polished look and
feel.Reports are how you present your information visually, where
you use charts and graphs.For information on creating forms and
reports, see the links in the Course Summary, and thank you for
your time.Thanks for taking these courses.
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Course summaryIntroduction to queries (Access basics, part
3)
The DesignerMulti-sourceOuter joinsUnrelated
sources4:454:452:504:455:24IntroductionThe basic processStart with
a question, identify tables or queries with data that answers the
question, create query, add data sources, fields, run. Use the
Query WizardCreate > Query Wizard.Select a query type >
OK.Select a data source (tables or queries), select your fields
> Next. Enter a name, select an option to open or modify >
Finish Use the query designerCreate > Query Design.Use the Show
Table dialog to add tables or queries.Double-click/tap, or drag and
drop fields to add to the design grid.Query multiple sources If you
use related tables, theyre joined. Joined fields in unrelated
sources must have matching or compatible data types; results should
make sense.Left outer join: All the data in the left-hand table,
only matches from the right. Right outer join is reverse. To add a
join: Drag and drop.To create the query: Add joined sources, add
fields, run.Intermediate tables If two unrelated tables are both
related to the same table, add that 3rd table to the query, then
query the unrelated sources.See alsoIntroduction to queriesCreate a
select queryJoin data sources in a queryApply criteria to a
queryCreate an Access formIntroduction to reports in
AccessIntroduction to expressionsMore training coursesOffice
Compatibility Pack
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