Using Microsoft Access

Transcription

1 Using Microsoft Access Creating Select Queries Norm Downey Chapter 2 pages and Chapter 3 pages

2 This PowerPoint uses the Sample Databases on the class website Please download them now 3 What is a Query? Queries allow the user to manipulate the data stored in tables Queries fall into two broad categories: Select Queries these answer questions by returning data subsets based on given criteria and are the most common types of queries Action Queries these allow the user to manipulate table data by appending, deleting, or updating data 4 2

3 The Select Query A select query is a way of asking a question of the data stored in a table or tables within a database Select queries can answer questions such as: List all employees by last name alphabetically. Which employees live in a specific Zip code? How many employees have a salary greater than $50,000? Which employees are assigned to which project? 5 The Select Query Select queries return only a subset of the data Allows the user to choose the data and the order of the data to be displayed The results of a query, sometimes called the return, answers the question Remember that data is not stored in query, it is merely a structured question of the data stored in the databases' tables 6 3

4 Download Sample Databases Be sure to Enable Content Once the database is downloaded, open it and take a look at the tables in both design view and datasheet view. Look at the types of data that the table stores and the values that are stored within the table. It is important to know what kind of data you are dealing with before you ask a question (or create a query). 7 Creating the Select Query To create a query, click the Create tab and then click Query Design On the Show Table dialog box, select the Employees table and click Add and then Close 8 4

5 Creating the Select Query This block is called a Field List and shows the names of the fields in the Employees table The area at the bottom is called the Query Design Grid. It is where the query is built from elements of the Field List 9 Creating the Select Query Now you can begin to add fields from the table in the upper portion of the design window to the lower design grid. There are three ways to do that: Click and drag items from the table in the upper half of the query design screen onto the design grid on the lower half of the design screen; Double click an item in the table in the upper half of the query design screen and that field will populate the next available field or; Use the drop down boxes in the Field line of the design grid on the lower half of the design screen to select the fields you want in your query. 10 5

6 Creating the Select Query Click on the View Button to see the results of your query Yes, you could use the RUN! Command to view your query results, but it s best to get into the practice of using View. RUN! combined with a an Action Query could have disastrous and irreversible consequences. 11 Saving the Select Query To Save the query, click the save icon in the Quick Access Toolbar. On the Save As dialog box, give your query a name that starts with the letter Q. Be descriptive in your names but don t use any spaces. 12 6

7 Saving the Select Query Q_EmployeeNames should now appear in the Objects Bar under Queries. If not, click on the All Access Objects drop down list arrow and choose All Access Objects 13 Sorting the Select Query Results We can improve the Q_EmployeeNames query by sorting the results. In the design grid, on the Sort row, we have three choices for sorting: 1. Ascending A to Z 2. Descending Z to A 3. (not sorted) this is used to remove an existing sort 14 7

8 Sorting the Select Query Sorting Ascending on Last Name produces only so-so results. Although everyone is sorted by last name, the staff are still out of order by first name. Notice that Donald Duck comes before Daisy Duck. Let s add sorts to both first and last names. 15 Sorting the Select Query Return to Design View by clicking the View command on the Ribbon s Home Tab. Use the drop down box to add Sort Ascending to both FirstName and LastName. 16 8

9 Sorting the Select Query the wrong way The results are disappointing. Steven, who should be first, is now at the bottom. What happened? Sorts go from left to right, so FirstName was sorted first and then LastName. This is NOT the right way to do this sort. Click the View command to return to Design View 17 Sorting the Select Query the right way! Uncheck the Show Box 1. Add FirstName to the design grid again be sure that it is to the right of the LastName field 2. Change the sort order for the left most instance of FirstName to (not sorted) 3. Keep the Sort Ascending for LastName 4. Add a sort to the second, right most instance of FirstName, but deselect (uncheck) the Show checkbox so this column will not appear in the results 5. LastName will be the first field sorted since it is the leftmost field with a sort 6. By including two FirstName fields we can arrange the sort correctly, and display the columns in the proper order 18 9

10 Sorting the Select Query The results are now correct. Steven Buchanan is at the top, Daisy Duck is the first of the Ducks and Michael Suyama is at the bottom. Note that the second FirstName field in the design grid does not display in the results, but is used for the sort. It does not display because we unchecked the Show box. Use the Save As Icon in the Quick Access toolbar to save this query as Q_EmployeeNamesAlphabetical 19 One Criteria Queries Text Criteria If we only wanted employees from a specific city in our results, we could use a text criteria to limit the results To do this Add City to design grid On the Criteria line, under City add the text Buena Vista Access will add quotes around it for you meaning that it recognizes this input as text You must spell it exactly correctly or the query s result will be blank Click the View command to see the results 20 10

11 One Criteria Queries Text Criteria 21 The results display only those employees in that live in the city of Buena Vista Text criteria could be use in any text field in the design grid. Other examples of text criteria in a select query would be: Mouse in the LastName field Pittsburgh in the CITY field TX in the STATE field in the ZipCode field remember that in this case Zip Codes are text, not numbers, and are identified by the double quote marks Save this query as Q_EmployeeNamesAlphabetical_BuenaVista Wildcards Wildcards take the place of one or more characters in the query s criteria * = Many characters? = One character In the sample above, under LastName, enter D* and hit enter. Access will finish it with the words Like and add quotes around the text D* This will return anyone whose last name starts with the letter D 22 11

12 Wildcards In this example, we use an * wildcard to represent many characters. By place a * at the beginning and end of the phrase blvd in the Address column to return all instances where an Address contains the acronym blvd Placing the * in front of and after blvd allows us the query to return any record that contains blvd, even if there are characters before it, or after it 23 Wildcards In this example, we use an? at the end of the criteria for ZipCode this will return any employee whose first four zip code digits are In the query results, the final digit varies because of the use of a wildcard

13 Comparison Operators in Queries Used with numbers (all types), currency and date/time fields Expression Example =10 All values equal to 10 <>10 All values NOT equal to 10 >10 All values greater than 10 >=10 All values greater than or equal to 10 <10 All values less than 10 <=10 All values less than or equal to 10 Is Null Used to find blank fields Is Not Null Used to find fields with data 25 One Criteria Queries Number Criteria We can also use number criteria to limit the results of our query. Add the Ratings field to the design grid Ratings are Singles (numbers with decimal values) that range from 0.00 to 4.00 Typically a range is specified when using number criteria, such as < 2 meaning all numbers less than 2 > 2 meaning all numbers greater than 2 Between 2 And 3 meaning all numbers greater than 2, but less than 3 It is rare to use an exact number because that would require an exact match and return very few results 26 13

14 One Criteria Queries Number Criteria Less than 2 Greater than 2 Select query using number criteria set to display all employees with a rating of less than 2. Select query using number criteria set to display all employees with a rating of greater than One Criteria Queries Yes/No Criteria In this query we include the field name Certified in the design grid and to set the criteria to Yes to return all those employees who are certified Only those employees who are certified appear in the results A checked boxes means YES (or True or On). An unchecked box means No (or False or Off) 28 14

15 One Criteria Queries Date Criteria We can also use date or time criteria to limit the results of our query. Add the BirthDate field to the design grid The BirthDate field use the Date/Time data type and stores dates as serial numbers which allows for date and time calculations It is rare to use an exact date or time because that would require an exact match and return very few results 29 One Criteria Queries Date Criteria Like numbers, a range is typically specified when using date/time criteria, such as 30 < #1/1/1981 meaning all dates before January 1, 1981 > #1/1/1981 meaning all dates after January 1, 1981 Between #1/1/1981# And #12/31/1990# meaning all dates after January 1, 1981 but before December 31, 1990 Do NOT enter the pound signs let Access do that for you 15

16 One Criteria Queries Date Criteria Results showing only those employees born in the 1980 s Save as Q_EmloyeeNamesAlphabetical_the80s 31 Queries with Ands and Ors Queries using Ands Condition 1 Condition 2 Outcome True True True True False False False True False False False False Queries using Ors Condition 1 Condition 2 Outcome True True True True False True False True True False False False AND versus OR Using AND to join criteria limits the results since it is necessary to meet all of the specified criteria Using an OR to join criteria expands the results since it is necessary to meet only one of the specified criteria 32 16

17 And Query Two Criteria joined by an And In this example we use two criteria joined by an AND therefore BOTH conditions must be TRUE in order to be displayed in the results Criteria 1 Ratings below 2.5 Criteria 2 Salary above $50,000 (note that we omit the dollar sign and comma in the query design grid) This query is asking the employees table, Which employees have ratings below 2.5 AND a salary above $50,000? 33 Or Query Two Criteria joined by an Or In this example we use two criteria joined by an OR therefore EITHER condition must be TRUE in order to be displayed in the results Criteria 1 Ratings below 2.5 Criteria 2 Salary above $50,000 (note that we omit the dollar sign and comma in the query design grid) This query is asking the employees table, Which employees have ratings below 2.5 or a salary above $50,000? 34 17

18 Queries with Ands and Ors Queries using AND Queries using OR And queries line up criteria across on the same line. Or queries stagger criteria using the criteria line and the or line. All the blank lines below the first or line in the design grid are for more Ors. 35 Using an OR on One Field To use two criteria one field using an OR, stack them vertically. This query shows an alphabetical list of our employees from Pennsylvania or Washington. After closing and reopening, Access may reorganize your query as shown 36 18

19 Parameter Queries Parameter Queries prompt the user for input Enter the prompt on the criteria line within square brackets Use a meaningful prompt If the user misspells the input no results 37 Creating Calculations in Queries In the design grid modify the existing Q_EmloyeeNamesAlphabetical query by adding the Dependents field from the field list In the next column, in the field cell, right click and choose Zoom 38 19

20 Creating Calculations in Queries using Zoom After entering the formula, click OK to close Zoom dialog box. In the Zoom dialog box enter the following text: Benefit Costs: [dependents]*1500 This text is in three parts: Benefit Costs this is a new field name that you have created by typing it in : the colon separates the new field name from the calculation [dependents]*1500 this is a calculation multiplying the value in the dependents field by 1500 note the square brackets they are used to designate this word as a field name Access will add these for you 39 Formatting Calculations in Queries Back at the design grid, right click Benefit Cost, choose properties and on the properties pane, set the format to Currency 40 20

21 Creating Calculations in Queries Save As Q_EmloyeeNamesAlphabetical_BenefitCost 41 Using the Expression Builder The expression builder allows you access to many prebuilt functions as well as individual fields from the databases tables This query will use the expression builder to use a nested IIf function to give a raise to staff with a rating greater than 2.5 and salary less than IIf has three parts: Logical Test True False Does this look familiar?? 42 21

22 Expression Builder Right click in field cell, choose Build On the Expression Builder, under Expression Elements, open Functions, Built-in Functions, under Expression Categories, choose Program Flow and under Expression Values, choose IIf function populated in the builder at top. 43 Expression Builder On the Expression Builder, select expression in the build area, under Expression Elements, open database, tables, choose table, then from Expression Categories choose rating by double clicking. Modify the expression to read [Employees]![Rating] >

23 Expression Builder Highlight <<truepart>> and insert a second, nested IIf function. Modify the expression to read IIf( [Employees]![Rating] >2.5, IIf( [Employees]![Salary] <50000, «truepart», «falsepart»), «falsepart») 45 Expression Builder IIf( Test [Employees]![Rating] >2.5, Truepart Nested IIf IIf( Test [Employees]![Salary] <50000, Truepart "Raise", Falsepart "Does not meet salary criteria"), Falsepart "Does not meet rating criteria") 46 23

24 Expression Builder 47 Using Microsoft Access Creating Select Queries Norm Downey 24