When you start Microsoft Access, the upper left of your screen looks like this.

Transcription

1 Basic Queries in Access 2010: Filtering Ira Chinoy / JOUR 772 & 472 / Philip Merrill College of Journalism Access is a program that allows us to examine the information in a database several different ways in effect, to interview a database. One of ways we can do this is to search for individual records that meet certain criteria. If we had a database of campaign contributions, this sort of query might be used to find each of the donors who gave to a particular candidate. If we had a database of restaurant inspections, the same sort of query might allow us to find all the restaurants that had a history of unsanitary conditions. This process of searching for specific records is referred to as filtering. In subsequent class sessions we will look at two other ways of exploring a database. One is summarizing for example, determining the sum of contributions received by each candidate. The other way of exploring records in a database is by linking or joining information contained in separate collections of data for example, finding individuals who are in both the database of registered school bus drivers and the database of traffic court cases. GETTING ORIENTED: Let s start by getting familiar with moving around in Access. When you start Microsoft Access, the upper left of your screen looks like this. If you click on File, the view will toggle back and forth between what you see above and this: 1

2 To open a file in, click on File and then Open Let s open a database of dam inspection records. It s named Dams98.accdb. The.accdb file extension tells us that this is an Access database file that can be used with versions 2007 or later. Access files from 2003 or earlier have an.mdb extension and can also be used with Access You will see this security warning: For data files we will use in this class, click on Enable Content after which you will see another warning: Click Yes. You will not see a box labeled Tables with one table in it, DAMS. An Access file is a container that holds a variety of objects, and it has a great many uses and functions. We will concern ourselves in this course with the basics. 2

3 If you click on the drop-down arrow to the right of the Tables label, you will see a list that includes two of the objects of interest to us in this course: Tables and Queries. The first, Tables, lets us see the names of specific data tables in the database or create new tables. Database files often contain more than one table that can be linked together, something we will learn later on. The second, Queries, refers to the questions we ask of the table or tables in the database. To see the tables and queries as we move along, we re going to click on the item at the bottom of the list that says All Access Objects. As we move along, the Queries we save for later use will also show up in this set of objects. The Tables and Related Views option is another way to see both the tables and any queries associated with them. For now, we will stick with All Access Objects. This database contains a single table named DAMS. If we double-click on DAMS, we can see the table or the part of the table that s visible. Use the Maximize icon to see the table in the fullest possible view: Here s what you will see: 3

4 If we scroll to the right, we can see the other columns in the database: In a database, the rows are called records and the columns are called fields. At the bottom of the screen is an important number, the number of records in the table. In this table, there are 1,644 records. That means the table contains entries for 1,644 dams. We will talk in class about the importance of the number of records, and we will talk about some of the issues associated with understanding what the fields in a table represent and what the entries in those fields mean. To close the database without exiting Access, click on File and Close Database. If you changed the width of columns for easter viewing, you will see this: You can click on Yes. 4

5 FILTERING: We re now going to turn to a different database to learn how to do filtering queries. We will be using a database of campaign contributions in class. It s called Contribs.accdb, and you will be downloading it from the class Web site. It is a portion of a database of campaign contributions made to candidates for the U.S. House and Senate from individuals listing South Florida addresses. It covers eight months starting in August (This is part of a database provided by the Federal Election Commission (FEC) to the National Institute for Computer-Assisted Reporting, and it is referenced in the optional textbook for this course.) EXAMINING THE DATABASE: Remember to select Enable this content when you get the initial security warning. The database contains two tables: Candidates and Contributions. For this exercise we are going to be using the Contributions table. EXAMINING A TABLE: When you get data from an outside source, you ll want to make sure that the number or count of records in what you see matches what the source agency listed as the number of records in each table. You will also want to look for such data integrity issues as whether there is consistency in the way the same information such as city names appears in different records and whether there are blank cells or null values. If you open up the Contributions table by double clicking on it. Use the Maximize icon here at the top of the frame that contains the table to work with the table in the largest possible view With the table open, you ll notice at the bottom of the screen that it has 3,374 records. You ll also see that this Contributions table does not actually have the names of the candidates receiving these contributions. Instead, there is an identification number for the candidate, which appears as the last column on the right, CAND_ID. 5

6 The other table, Candidates, has information used to link a candidate s ID number (assigned by the Federal Election Commission) to the candidate s name. We will learn in a subsequent exercise how to join these two tables using that identification number. DOCUMENTATION: To make sense of the field names you see in Contributions, you ll need the documentation the record layout, or list of fields, and a code sheet or data dictionary that explains any codes that appear in the table. Here s the basic documentation for Contributions: FIELD NAME TYPE SIZE DESCRIPTION LAST Text 20 Last name of contributor REST Text 20 Rest of contributor name CITY Text 18 Contributor city STATE Text 2 Contributor state ZIP Text 5 Contributor zip code OCCUPATION Text 35 Contributor occupation CONT_DATE Date 8 Date of contribution AMOUNT Number 8 Amount of contribution (or refund if the number is negative) PRIMGEN Text 1 Election type P = Primary G = General R = Runoff CAND_ID Text 9 FEC Candidate ID If you were using this database for a story, you would be able to learn a lot more about it from more extensive documentation, from the source of the data, and perhaps from other reporters who had used it. For example, you might learn that the Occupation field sometimes contains the donor s type of work and sometimes the name of the donor s employer or business. Before we take the next step, close the Contributions table. Use the X button on the upper right of the table, but not the red X button at the top of the screen, which closes the program). Next, let s look at the landscape at the top of your computer screen. 6

7 Access 2010 has a two-tiered menu system for locating commands. First, there is a row of tabs: And these sit atop a ribbon of icons that are different for each tab. If we click on the tab that says Create, we see this set of icons in the ribbon: The sixth icon from the left is Query Design. We will click on that. Once we do that, we have a choice to make. Which table or tables are we going to query? Let s say we wanted to get a listing, in alphabetical order, of all the names of the donors. We d want the Contributions table. So click once on Contributions and then click Add and then Close. Now you see something that looks like this (and use the Maximize icon again): At the top is the table you have chosen Contributions and there is a box that will let you scroll through the field names in that table. The area below is called the Query Grid. You will use it to build queries for interviewing the database. We ll learn the meaning of its parts as we work with Access: Field, Table, Sort, Show, Criteria, and one labeled or (for adding more criteria, or search terms and conditions) 7

8 SELECTING FIELDS AND SORTING RECORDS: You re ready to begin building queries. We want to start by getting field names from the list in the Contributions table down into the Field line in the query grid. There are three ways to do this. For example, to get LAST (i.e. last name of the donors) into the Field line, we can do one of the following: (1). We can move the cursor to LAST in the list of field names, hold the left mouse button down to select LAST, and then continue to hold down the button as we drag that field name to the Field line in the query grid, where we release the button. (2). Or, we can double-click on LAST in the list of field names for the Contributions table. In either of these cases, LAST will appear in the query grid on the Field line, and below it you will also see the name of the Table from which LAST came, Contributions. The third way to get a field into the query grid is to click in an empty cell on the Field line in the grid. A small drop-down arrow appears. If you then click on the arrow, you will get a list of field names from which to choose. You can select the field you want from that list by clicking on the field name. The small box in the Show line will get a check mark when you add a field to the grid, indicating that this field will be displayed in the answer you get from your query. If we add the first names (REST), city, state, contribution amount and date, we see this: If we want to sort these by last name, we can click on the Sort line under LAST in the query grid and we will get three choices. If we pick Ascending, we will be able to sort the data from our query in alphabetical order: 8

9 You may have noticed that as we were building our query, the ribbon changed to from the Create tab to the Design tab, with an extension labeled Query Tools: To Run the query that is, to see the answer to our question we click on the button that shows a red exclamation mark: Here s what we get: You ll notice at the bottom of the screen with the list of contributor names is the total number of records returned by the query. It s 3,374 the total number of records in the Contributions table. The number is 3,374 because our query, while selecting only certain fields, did not set no Criteria to select some records and disregard others. We ll do that in a minute. To get back to the Design View to modify our query, click on the View button: 9

10 CRITERIA FOR SPECIFIC RECORDS: To get all the donors in this database who live in a place called Atlantis (really), we d type Atlantis in the Criteria line for the CITY field. We can add in the last name, first name, amount and state (they should all be from Atlantis, Florida, since this is a database of South Florida donors, but it never hurts to be cautious). Here s the query: You ll notice that if, after typing in Atlantis, you click on another cell in the query grid, Access adds the quotation marks around Atlantis. This is a signal that you are searching for text rather than a number or a date. Here s what the query looks like now: When you run the query, here s what you get: The number on the bottom of the screen 14 in this case tells you the total number of records returned by your query. Access shows a blank row underneath the 14 th record -- the one with the asterisk -- but it is not part of your answer set. We didn t get all 3,374 records because our query, by setting criteria, returned only some records. 10

11 AMOUNTS: You could search for all the contributions over or under a certain amount by using these operators: the greater than sign: > the less than sign: < For example, the query below will return records for contributions greater than $500. We will remove Atlantis from the Criteria line for CITY We will put >500 in the Criteria line for AMOUNT. Note that you don t use quotation marks or a dollar sign when setting the criteria line for a numeric field. We will choose Ascending on the Sort line for AMOUNT. And we will remove the sort Ascending from LAST by selecting (not sorted) on the Sort line for LAST. The result: If you were searching for amounts of 1,000 or more, you would type this into the query grid WITHOUT THE COMMAS. Here are some other operators you can use. A tip sheet of operators and special characters is included in this handout. Greater than or equal to: >= Less than or equal to: <= 11

12 DATES: We can also search for contributions on a particular date. Let s say we wanted to look for all the contributions on September 8, We could type that into the Criteria line in any number of ways, such as these: 9/8/95 Sept. 8, 1995 Sept Sept-95 Access would take what we typed in and revise it to the format below after we moved off that cell. The hash marks (#) are a clue that this is a date field (not numbers or text). We see our entry this way: #9/8/95# Here s the result: BETWEEN: You could also search for all records that fall between two dates (and including those two dates). To fine the ones between Christmas, 1995, and New Year s Day, 1996, you would type this: Access would change the query to look like this: Here s the result: 12

13 NARROWING YOUR QUERY: Think AND and use the same criteria line You might be interested in finding donors who meet two or more criteria: for example, all the people who listed their occupation as student and listed their city as Palm Beach. (NOTE: Queries of text fields are not case-sensitive, as you ll see below). First, let s clear the grid empty out the query grid so we can create a fresh query. You need to be on the Home tab. And in the Sort & Filter area, you need to click on Advanced From the menu for the Advanced, click on Clear Grid. NOTE: To have this command easily accessible in the future, you can right click on Clear Grid and then pick Add to Quick Access Toolbar. The Clear Grid button (looking like a handwritten X ) should now appear near the upper left of your Access 2010 screen and stay there. After you select Clear Grid, the table you are using for your query will remain, but the part of the grid used to build the queries by choosing fields and criteria will be emptied out: OK, back to our query (and back to the Design tab on the ribbon). We are interested in donors who are students and are from Palm Beach. The operative word in our question is and, and the query looks like this: 13

14 Notice that student and palm beach appear on the same line, which will show any record in which the donor s occupation is student and the donor s city is Palm Beach. A student living outside Palm Beach would not appear in the answer, nor would a non-student from Palm Beach. Here s what you get five records: Do you have any questions about what you ve found so far? How might you go about answering them? 14

15 WIDENING YOUR QUERY: Think or. and use separate criteria lines In contrast to that way of constructing a query using this and concept, if you wanted to find any record in which the donor s city is Palm Beach or the donor s occupation is student, you would need to put these criteria on separate criteria lines, as follows. In this query, the results are sorted first by last name, then by first name, and then by date: Notice that we now get many more records than our original and query 272. The results include: donors from Palm Beach who are not listed as students donors who are listed from Palm Beach but are not students and donors who are both from Palm Beach and listed as students 15

16 FINDING RECORDS USING NOT Let s say you wanted to find all the students who lived outside Palm Beach. You could use the not operator, as follows and remember that what you are building, in this case, is a query that includes the and idea: one that will return any record in which the occupation is student and the city is not Palm Beach. If we type not palm beach in the criteria line, Access changes it to Not palm beach. The word not is recognized as an operator, and palm beach is recognized as text. Here s the result students from everywhere except Palm Beach 16

17 OPERATORS WITHIN A SINGLE FIELD: Let s say you work for a paper near Lake Okeechobee and you cover the communities of Pahokee and Belle Glade. You could find any donor who listed his or her residence as either Belle Glade or Pahokee and you could do this one of two ways. The first is the way you learned above: But since you are establishing criteria for a single field, you could also set up the same query this way: The result: Notice what happens if you use and instead of or when you construct the query. If you set it up this way: Here s what you get: nada. Why? Because it is logically impossible to have any donor whose city is listed precisely as Pahokee and, in the same spot, also listed precisely as Belle Glade This is a common mistake. There are definitely occasions when you might use and within a single cell, but only when you are using wildcards (more on wildcards below). 17

18 USING WILDCARDS: Access is quite literal. If you plug in Miami Beach as the criteria for the city, it will return the 74 records in which the city is listed precisely as Miami Beach but it will not return the record with the city listed as Miami Bch. You remember that we have talked about data integrity, and this is an example of dirty data two entities that are the same but, in this case, spelled differently. That s where wildcards come in. They let you search for parts of words. The two most common are the asterisk (*) and the question mark (?). The asterisk (*) lets you search for any number of characters or numerals. For example, in the criteria line for the city field: Miami B* would return records with Miami Beach or Miami Bch *Miami B* would return records with the city listed as one of the following: Miami Bch Miami Beach N Miami Beach No Miami Beach North Miami Bch North Miami Beach Boynt?n Beach returns Boynton Beach and Boyntin Beach (misspelled) but does not return Boynton Bch or Boyton Beach (also misspelled). You ll note when you run a wildcard query that after you type in *Miami B* in the criteria line Access changes it to this: Like *Miami B* 18

19 NULL VALUES An empty cell in a record is called a null value. Sometimes you may want to look at the records that have null values in a particular field, or you may want to look at records that only have something entered in a particular field. You would use the criteria Is Null for the former and Is Not Null for the later. For example, you could use Is Null (don t use quotation marks) to bring back all records in which nothing is entered for the donor s occupation: Or you could bring back only those records that DO have something listed for the occupation by using Is Not Null: 19

20 A WORD OF CAUTION: If you build a query that takes up more than one Criteria line, you need to be careful. Here are some examples for you to study. I suggest you look at them closely until you get the distinction between them: The following brings back any records with the words housewife or homemaker appearing in the Occupation field (and sorted here by last name and then by first name). We get 282 records The following brings back anyone with the words housewife or homemaker appearing in the Occupation field (sorted here by last name and then by first name) AND who is from Palm Beach. Or, stated another way, we get anyone who is a homemaker from Palm Beach OR a housewife from Palm Beach: The result: 32 records: 20

21 But the following is different: It brings back any record for which at least one of the following (A or B) is true: (A). The occupation is housewife AND the city is Palm Beach OR: (B) The occupation is homemaker regardless of that person s city of residence. The result: many more records, 201. If you explore the results, you will see homemakers from all over Florida, but the only time housewife is listed is when the city is Palm Beach. The point here: When you are building queries with complex conditions, be sure that they are asking the question you mean to ask! 21

22 SAVING YOUR QUERY: Let s say that we want to save our query of student donors: From the quick access menu at the top of the screen, click the save button: This brings up a small dialog box for naming the query, with the default name Query 1 appearing as the suggested name. Replace Query1 in the dialog box with the name you are giving the query such as Student donors and then click OK. The query is now saved to be run again. You will find it under Queries in the list of Objects on the left of your screen. You can view the query grid for that query by rightclicking Student Donors once and bringing up a menu. Then click on Design view to see the query. Or you can run the query by clicking on Student Donors twice. 22

23 Operator / Special Character [No operator] * at the beginning and end of a text string * at the beginning of a text string * at the end of a text string OPERATORS AN SPECIAL CHARACTERS IN ACCESS Examples of criteria Smith Smith *farm* Like *farmer* *house Like *house house* Like house*? s?n Like s?n AND [In some cases the ampersand ( & ) functions like AND] Operator / Special Character OR NOT < > [see note for exception] XOR [either or] *Patrick* and *Ward* Like *Patrick* and like *Ward* Examples of criteria Smith or Jones Smith or Jones Not Smith < > Smith Not Smith *New* XOR *York* What it does In a name field, brings back any record where the name is Smith (but not Smithsonian or Robert Smith) Wildcard returning any text string that includes farm: Farmer Sugar Cane Farmer State Farm Insurance Returns any text string then ENDS with house: White House House The Big House But not: Housewife Returns any text string that BEGINS with house Housewife House of Pain But not: White House The question mark is a wildcard that stands in for any single character: Sun Son In a field that had first and last names, would bring back: Ward Patrick Patrick Ward Patrick A. Ward What it does In a field of last names, this brings back any record for Smith or for Jones Brings back all names except Smith. Note: < > does not substitute for NOT when combined with LIKE; you can use NOT LIKE *Smith* but the following does not work: <> LIKE *Smith* Returns a cell that contains either New or York but does not contain both New and York (so it would not return New York). Brings back any record that has Smith, Jones, or King as the field showing last names. IN IN (Smith, Jones, King) IN( Smith, Jones, King ) BETWEEN Between 100 and 500 Selects any value from 100 through 500 < <10 Returns any value less than 10 <= <=10 Returns any value less than or equal to 10 23

24 > >1000 Returns any value greater than 1,000 [Note: Do not use a comma when writing a number in a query, such as >1,000] >= >=1000 Returns any value greater than or equal to 1,000 [Note: Do not use a comma when writing a number in a query, such as >1,000. Access doesn t know what you are talking about.] Is Null Is Null Returns any record for which there is no data in the field you are searching. For example, if you were searching on a field recording someone s age, putting Is Null in the criteria line of the query would bring back any record in which no age was listed. Is Not Null Is Not Null Does the opposite of the example above brings back records in which some value has been entered in the age field. Revised