Microsoft Access Lesson 2: Retrieving Information from a Database

Transcription

1 Microsoft Access 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.mdb) 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) Select the Last Name column and click on the Find icon. In the window that pops up, enter Bullock in the Find What: text box. Select tblemployees in the Look In list. Click on Find Next. When you find the record, edit it to reflect the new personal information. 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 Filter by Selection icon. You should see only the NC employees displayed. Click on the Filter icon to remove the filter. Practice: List only the employees who work in the department with ID 106. Practice: List only the employees who live in Spartanburg and who work in the department with ID

3 Filtering by Form You also can do more complex filtering than by selection. Suppose, for examplee that you would like to see only those employees who have been hired after 1/1/2000. Click on the Filter by Form icon. You will see a blank form showing each of the fields. Enter >1/1/2000 in the Hire Date field. Then click on the Filter icon. 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 (Filtered) in the window status bar. Click on the Filter icon again to remove the filter. 3

4 A wide variety of filtering expressions is available. Consult Access Help s Filtering Data topic for more details and examples. Practice: Use Filter by Form to list only the employees living in Spartanburg who weree hired before January 1, Practice: Use Filter by Form to list all the employees whose last name starts with W. Practice: Use Filter by Form to list the all employees who live on Tio Lane. 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 one of the cells in the Last Name field column. Then click on the Sort Ascending icon. You will now see that data sorted by last name. Practice: Sort the data by ZIP Code. Practice: Sort the data so that it again is listed according to Employee ID. 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-lifee databases, such as Banner, can contain thousandss 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. Click on Queries in the Objects list. Double-click on Create query in Design view. 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. Alll of this information is in tblemployees. Select this table and click on the Add button. Then click on the Close button. 5

6 You should see the field names in the table displayed at the top of the Select Query window. Grab the junctions between sections of this window and stretch sections so that the window looks like the picture at the right. 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 willl use to design your query. We want to add the fields for our query to the Design Grid. The query is What are the First Names and Last Names of Employees living in Spartanburg with a Hire Date before 1/1/2000? 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. 6

7 Do the same for the other Fields you need. 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. 7

8 We now have the conditions for the query set. To execute the query, click on the Run Query icon in the main toolbar You will see a table with the results of your query. To save the query, click on the Save icon. You will be prompted to name the query. Let s name it qryearlyhire. Note: After you have run a query, you can toggle back and forth between the Datasheet and Design Views of the query using the appropriate icons, just as you did with tables. 8

9 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 characters 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 105. 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. 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 comparison operator and run the query. Save the query as qrysc2004_1. 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_2. 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. 9

10 Practice: Design a query that lists all addresses with Zip codes beginning with 293. Run and save the query as qryzip293. 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. Using this interface, you have constructed a query in Structured Query Language (SQL). You can view the SELECT statement by opening the query in design view and then selecting SQL View from the View Tool. The SQL associated with qryearlyhire is: SELECT tblemployees.lastname, tblemployees.firstname, tblemployees.city FROM tblemployees WHERE (((tblemployees.city)="spartanburg") AND ((tblemployees.hiredate)<#1/1/2000#)) ORDER BY tblemployees.city, tblemployees.hiredate; Fortunately, Access lets you construct a query by example by filling out a form and you don t have to learn SQL to use its power. 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. If this is the case, and if the fields contain identical data, then the tables may be joined automatically when you add the two tables to a query. If not, then you may specify the fields to be joined. 10

11 Digression: Disabling Autojoins Note: If you do not want Access to automatically join tables, choose Tools, Options from the Access main menu. In the Options window, select the Tables/Queries tab. The Enable AutoJoin box probably will be checked. Uncheck the box if you do not want joins to be created automatically. Create a new query in Design View. In the Show Table window, Addd both tblemployees and tblsalaries to the query. Then Close the Show Table window. 11

12 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. 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. 12

13 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. 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. Consider the table, tblsalaries, which shows yearly salaries for each employee. 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. 13

14 The first part on the left of the colon is the name of the calculated field. Anything in brackets is an existing field. Thus MonthlySalary: [Salary]/12 means define a calculated field named MonthlySalary, that is calculated by dividing the Salary field by 12. Sort on the MonthlySalary field in Descending order. We need to format this field so it will display as currency. Click on the calculated field cell to select it and then click on the Properties icon in the main toolbar. In the Field Properties window, set the Format to Currency. Also make the field s caption Monthly Salary. Run and Save the query. 14

15 Which Way of Retrieving Information is Best? 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. 15