SQL represents one of the standard languages used for database management purposes, while MySQL, instead, is the software using that specific language.
The query database feature is equal in necessity to data storage capability. Thus, a number of query languages have been developed for different database engines and purposes, but SQL is by far the most ubiquitous and well-known. In fact, rookie database administrators often are surprised when they learn about the existence of other query languages. Query languages generate different data types according to function.
For example, SQL returns data in neat rows and columns and is very similar to Microsoft Excel in appearance. Other query languages generate data as graphs or other complex data manipulations, e.
For example, a SQL manufacturing company query may reveal that monthly sales peak in June and July, or that female sales representatives continually outperform male counterparts during holiday months. A database can be queried by less experienced users who are not trained in a specific query language. The field is now moved to the right. Now, you're asked to select the field that you want calculated in the query on the left. You're also asked to select a function from the right that will calculate and put data in the query.
Above you'll see a picture of our query. You can also see the number of ISBNs under the corresponding author. However, let's play with our Books table to show you even more what a crosstab query can do. Just keep in mind that these are real book titles and authors, but fictional prices. Let's do another crosstab query. Our row headings and column headings will stay the same as they were in the other query. The only difference is in the screen where we select the Fields and Functions, we select Price and Avg.
You can also use a query to find duplicate data in your tables. This makes normalization easier. If you want the query to show any other fields, pick those in this screen. Perhaps we wanted to see book titles beside duplicate authors.
You don't have to select anything. We can see the duplicate data, along with the titles as we requested to show alongside that information. If you want to compare tables to identify records in one table that don't have any corresponding records in another table, you use an Unmatched Query. Let's learn how to do this. Go to the Create Tab and click the Query Wizard. By now, you know exactly where that is. Now, select the table that has unmatched records. For example using our tables , if we had a list of books in our Books table, but there wasn't an order for that book in the Orders table, we would select the Books table.
Now, find fields that the two tables have in common as shown below. They may already be selected, as they are related. In this case, we would select the ISBN fields.
As you can clearly see, you can use queries to find data in your tables or other queries. When you filter data, only the records with values that you specify will show. The rest of the data will remain hidden unless you remove the filter. Access has filters that are built into every view for you. If you can use the filter or not depends on the type and values of the field. For example, you can't filter columns in datasheets or controls in forms that are bound to expressions.
Let's say we want to view books in our Books table that cost a certain price. To do this, go to the Home tab. First, we're going to go back to our table and select the Price column. Queries are a way of searching for and compiling data from one or more tables. Running a query is like asking a detailed question of your database. When you build a query in Access, you are defining specific search conditions to find exactly the data you want.
Queries are far more powerful than the simple searches or filters you might use to find data within a table. This is because queries can draw their information from multiple tables. For example, while you could use a search in the customers table to find the name of one customer at your business or a filter on the orders table to view only orders placed within the past week, neither would let you view both customers and orders at once.
However, you could easily run a query to find the name and phone number of every customer who's made a purchase within the past week. A well-designed query can give information you might not be able to find out just by examining the data in your tables.
When you run a query, the results are presented to you in a table, but when you design one you use a different view. This is called Query Design view , and it lets you see how your query is put together. Click the buttons in the interactive below to learn how to navigate the Query Design view. Click the View drop-down arrow to switch to another view of your query. In most cases, you will only need to use two main views: Datasheet view and Design view.
Datasheet view lets you view your query results in the form of a table. If you use fields from data sources that are not related to each other, the Query Wizard asks you if you want to create relationships.
The wizard opens the Relationships window for you, but you must restart the wizard if you edit any relationships. Therefore, before you run the wizard, consider creating any relationships that your query needs. For more information about creating table relationships, see the article Guide to table relationships. On the Create tab, in the Queries group, click Query Wizard. Under Available Fields , double-click the field to add it to the Selected Fields list.
If you did not add any number fields fields that contain numeric data , skip ahead to step 9. If you added any number fields, the wizard asks whether you want the query to return details or summary data. If you want to see individual records, click Detail , and then click Next. Skip ahead to step 9.
If you want to see summarized numeric data, such as averages, click Summary , and then click Summary Options. In the Summary Options dialog box, specify which fields you want to summarize, and how you want to summarize the data. Only number fields are listed. Sum The query returns the sum of all the values of the field. Avg The query returns the average of the values of the field.
Min The query returns the smallest value of the field. Max The query returns the largest value of the field. If you want the query results to include a count of the records in a data source, select the appropriate Count records in data source name check box.
If you added a date-time field to the query, the Query Wizard asks you how you would like to group the date values. Note: In Design view, you can use an expression to group by any time period you want, but the wizard only offers these choices.
On the last page of the wizard, give the query a title, specify whether you want to open or modify the query, and then click Finish. If you choose to open the query, the query displays the selected data in Datasheet view. If you choose to modify the query, the query opens in Design view. You can use Design view to manually create a select query. When you use Design view, you have more control over the details of the query design, but it is easier to make design mistakes, and it can take longer than using the wizard.
Step 1: Add data sources. Step 2: Join related data sources. Step 3: Add output fields. Step 4: Specify criteria. Step 5: Summarize data.
Step 6: View the results. When you use Design view, to add data sources, you add the data sources and fields in separate steps.
However, you can always add more data sources later if you want. On the Create tab, in the Other group, click Query Design. Double-click each data source that you want to use or select each data source and then click Add. When you add the data sources, if the sources already have relationships defined between them, those relationships are automatically added to the query as joins.
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