Microsoft Access 2007 Lesson 2: Retrieving Information from a Database

Transcription

1 Microsoft Access 2007 Lesson 2: Retrieving Information from a Database In this lesson you will learn how to construct queries to retrieve information from a database. It uses the example database (ExampleDB.accdb) you saved on your H drive. Navigation Buttons Open the tblemployees table in the Datasheet view. At the bottom of the page, you will see a set of Navigation buttons. These buttons are useful for moving around in a large database. Try them. You can enter a number in the Record Box to move to a particular record. Finding a Record in a Table Entering the number in the Record Box will move you quickly to a record in a table. On the other hand, it probably is more likely that you will know something else about the records a name, an address, etc. rather than the record s number. In this case, you need to find the record. Suppose that Annie Bullock has changed her name, address, and phone number following her marriage. Her new personal information is shown below: Annie Rassmussen, 423 Poplar Avenue, Roebuck, SC (864) We want to find the last name Bullock. Select the Last Name column. Choose the Home tab and click on the Find icon. In the window that pops up, enter Bullock in the Find What: text box. Select Last Name in the Look In list. Click on Find Next. When you find the record, edit it to reflect the new personal information. 2/9/2008 1

2 Filtering by Selection Another way to search for data in a large database is to apply filters that restrict the information that is visible in the table. This does not remove information from the table in the database, but merely hides information that is irrelevant to a search. One way to filter data is to select the criterion from the table that you want to use as the restriction. Suppose, for example that you want to view the records of all employees living in North Carolina. Click on one of the NC cells in the State field and then click on the Selection Filter button. In the menu that appears, click on Equals NC. You should see only the NC employees displayed. Click on the Toggle Filter button to remove the filter. In Class Practice: List only the employees who work in the department with ID 106. In Class Practice: List only the employees who do not work in the department with ID 106. In Class Practice: List only the employees who live in Spartanburg and who work in the department with ID /9/2008 2

3 Filtering by Form You also can do more complex filtering than by selection. Suppose, for example that you would like to see only those employees who have been hired after 1/1/2000. Click on the Advanced Filter button and Clear All Filters. Then choose Filter by Form under Advanced Filters and enter >1/1/2000 in the Hire Date field. Click Advanced Filter and Apply Filter/Sort. The table of filtered data now will be displayed. In this case only employees with hired dates after January 1, 2000 will be shown. The fact that the data is filtered is indicated by the Funnel icon by Hire Date and the word Filtered near the navigation buttons. Click on Toggle Filter to remove the filter. 2/9/2008 3

4 A wide variety of filtering expressions is available. Consult Access Help s Filtering Data topic for more details and examples. In Class Practice: Use Filter by Form to list only the employees living in Spartanburg who were hired before January 1, In Class Practice: Use Filter by Form to list all the employees whose last name starts with W. (Remember that an asterisk often is used as a wild card symbol.) In Class Practice: Use Filter by Form to list the all employees who live on Tio Lane. In Class Practice: Use Filter by Form to list all employees who will celebrate ten years with the company this year. Sorting Records in a Table If all the information you need is in one relatively small table, the quickest way to find information may be to sort the records in the table. Open the tblemployees table in ExampleDB, if it is not already open. The data currently is sorted by EmployeeID in the left column. Suppose that you would like to alphabetize the list according to employee s last names. Click on the Last Name field. Then click on the Sort Ascending icon. You will now see that data sorted by last name. P r In Class Practice: Sort the data by ZIP Code. In Class Practice: Sort the data so that it again is listed according to Employee ID. 2/9/2008 4

5 Retrieving Information with Queries One of the most powerful features of Access is the ability to create queries to help you find information. We will use the ExampleDB database to illustrate queries. Retrieving information from this database, which is made up of only two relatively small tables, may seem trivial, and it really is you can merely look at the tables. Keep in mind, though, that real-life databases, such as Banner, can contain thousands of large tables and millions of records. Queries are the only practical way to retrieve information from such large databases. Suppose you would like to display the first and last names of all employees living in Spartanburg who were hired before 1/1/2000. We would like the list sorted in ascending order by hire date. Open ExampleDB if it is not already open. Under the Create tab, click on Query Design. First we must specify which table contains the information we need. In the Show Table window that appears, you should see a list of tables in the database under the Tables tab. We need information about the city in which employees live and their hire date for our search. All of this information is in tblemployees. Select this table and click on the Add button. Then click on the Close button. 2/9/2008 5

6 The Query window has two sections. 1. At the top you see the fields in the table(s) you have selected to use in the query. Note that the actual names of the fields are listed rather than their captions. 2. At the bottom you see the Design grid that you will use to design your query. We want to display the first and last names of all employees living in Spartanburg who were hired before 1/1/2000. We would like the list sorted in ascending order by hire date. The fields we need to include in this query are shown below along with the three conditions (City = Spartanburg, Hire Date before 1/1/2000, sorted by Hire Date) EmployeeID (the primary key in the table) FirstName LastName City = Spartanburg HireDate = < 1/1/2000; Sorted First, select EmployeeID from the list of field names. Hold the mouse key down on the arrow and drag it down to the first Field in the Design grid. Do the same for the other fields needed for the query. 2/9/2008 6

7 We now have the fields in the Design grid. Next we will enter the conditions. First, enter Spartanburg as the criterion for the City field. Next, move the cursor over to the Hire Date field column. Note that Access automatically surrounds Spartanburg with quotation marks, indicating that it is a character string value. Enter <1/1/2000 as the criterion for the Hire Date. When you move the cursor to another cell, note that Access automatically surrounds 1/1/2000 with pound signs, indicating that it is a date. Finally, click on the Sort cell in the Hire Date column. You will see a small menu icon appear in the right side of the cell. Open the menu and select Ascending. We now have the conditions for the query set. To execute the query, click on the Run button. The results of the query will be shown in the Datasheet View... 2/9/2008 7

8 After you have run a query, you can move back to its Design View using the View menu. To save the query, click on the Save icon. You will be prompted to name the query. Let s name it qryearlyhire. Close the query by clicking on the Close icon in the upper right corner of the query window. DO NOT close the database. Comparison Operators and Wild Cards The hire date criterion in the above example used a comparison operator ( < for less than ). The table below lists other comparison operators that can be used to specify criteria in a query. Comparison Operator Meaning Example = Equal to = 100 > Greater than > 100 < Less than < 100 >= Greater than or equal to >= 100 <= Less than or equal to <= 100 <> Unequal to <>100 Between... and... Between two numbers Between 100 and 200 You also can use wild cards to match text with patterns. Wildcard Symbol Meaning Example * One or more characters r*g will find rig, rag, ring, rung and running? One alphabetic character r?g will find rig and rag, but not ring or rung. [ ] Any character(s) within the brackets r[ia]ng will find ring and rang, but not rung [! ] Any character(s) not within the brackets r[!ia]ng will find rung, but not ring and rang [ - ] Any character within a range ra[l-p] will find ram, ran and rap, but not rag or rat. # Any single numeric character 10# will find 101 and /9/2008 8

9 When you enter an expression that contains a wildcard, Access automatically places like in front of the expression: like r*g for example. An expression containing a wildcard must have quotation marks around it. In Class Practice: Suppose you would like to list all employees (sorted in ascending order by last name) who live in SC and who were hired in Design a query for this using a comparison operator and run the query. Save the query as qrysc2004. In Class Practice: Suppose you would like to list all employees (sorted by last name) who live in SC and who were hired in Design a query for this using a wild card symbol and run the query. Save the query as qryall2004. In Class Practice: Design a query that lists first and last names of all employees who live in Spartanburg or in Greer. (Hint: Look at the row below the Criteria: row in the Design grid.) Run and save the query as qrysptbggreer. In Class Practice: Design a query that lists all addresses with Zip codes beginning with 293. Run and save the query as qryzip293. (Hint: if you use wildcards, use the form Like..... ) In Class Practice: Design a query to construct the data needed for a company directory. This is a list of employees sorted alphabetically by last name. Two employees with the same last name should be listed in order of their first names (and middle initial, if applicable. The rest of a listing should include address, city, state, ZIP code, and phone number. Name this query qrydirectory. (Hint: When sorting on more than one field, the field to be sorted first must be listed first in the query.) Listing Database Objects At this point, only tables probably are listed in the left of the Access window. Now that we have created a query, we would like to include it in the list. Click on the downward arrow icon to display a menu of objects to list. 2/9/2008 9

10 Select All Access Objects to display the queries along with the tables. Queries Using More Than One Table Most real-life relational databases are made of many tables and queries of often will involve more than one table. We will use EmployeesDB to illustrate how to create queries from multiple tables. Suppose you would like to list the salaries of all employees whom have been hired on 1/1/2004 and later. You would like to see their first and last names, their salaries and when they were hired. You want the records displayed with the highest salaries first. When we plan this query, we realize that the information we need is contained in two tables tblemployees and tblsalaries. To use two or more tables in a query, we must create a join between the tables. Usually one of the fields you are using for the join will be a primary key. Create a new query in Design View. In the Show Table window, Add both tblemployees and tblsalaries to the query. Close the Show Table window. 2/9/

11 Grab the Employee ID field name in the tblemployees list, hold the mouse key down, and drag it over the Employee ID field in the other list. Drop it there to join the two fields. When the two tables are joined, you will see a line connecting the two fields. This indicates that the joined fields in the two tables represent the same variable. By joining the fields, we have related the tables to each other. This is the origin of the term relational database. Drag fields down from the two tables as shown here. Note that we are using fields from both tables. Add the Sort and Criteria needed for your query. When you are ready Run the query. The results of your query should look like this. Save the query as qryafter2003salaries. 2/9/

12 In Class Practice: Create a query that will list the names of all members of the department with ID 102. Include the name of the department. Sort the last names in ascending order. Run and Save the query. In Class Practice: Create a query that will list the names of all members of the purchasing department and show if they are exempt or nonexempt from overtime pay. Sort by exempt or nonexempt status. Run and Save the query. Calculated Fields You also can include calculated fields in your queries. Suppose that you need to display each employee s full name and their monthly, rather than yearly, salary. You would like the list sorted by monthly salary in descending order. Open the ExampleDB database and create a query using the tables tblemployees and tblsalaries. Drag the fields that you need into the Design View grid. Include the Salary field, which we will use to calculate the monthly salaries. We don t want to display the Salary field, so uncheck the Show box for the Salary field. In the empty field next to Salary, enter the following expression: MonthlySalary: [Salary]/12 This is a calculated field. Sort it in Descending order. 2/9/

13 Right-click on Monthly Salary and select Properties from the menu. In the Property Sheet format the calculated field as Currency. Run and Save the query. What is the Best Way of Retrieving Information? In this lesson, we have learned about several different ways of retrieving information from a database Finding, Filtering, Sorting, and Queries. At this point it is a good idea to sit back and ask which is better. The answer depends on the situation. Finding is useful when you need to work with one specific record in a single table. If you need to change something in one specific record, a name for example, it usually is easiest to find it. Sorting is only useful for small tables. If you are working with a large table with thousands of records, it may be difficult to find information even after it has been sorted. Using a Filter or Sorting is faster than creating a query. If you need a quick and dirty way to retrieve information from one table, you might think about Filtering or Sorting. You can save queries. If you want to retrieve the same type of information more than once, creating and saving a query is the way to go. You can create queries involving multiple tables. If the data you need to retrieve is stored in more than one table, you will need to write a query to retrieve it. You can create reports based on queries. In the next lesson, you will learn how to write a report based on an existing query. 2/9/