Lab #3 Querying Data
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Transcript of Lab #3 Querying Data
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LAB #3QUERYING DATA
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Delete and update
Delete a record
Update a record
DELETE FROM vet_apptWHERE vet_appt_id = 3;
UPDATE animalSET’ gender = “MS”WHERE animal_id = 3
What would happen if you didn’t include a where clause with a delete or update record command?
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Query Data From Database
We use the SELECT statement to retrieve information from the database.
SELECT attribute/s
FROM table/s
WHERE (condition)
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Simple Select
List all the record s (rows) and all attributes (columns) in table:
* - WILDCARD
SELECT * FROM tableName;
Select * from animal
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Select Attributes/Fields
SELECT fieldNameA, fieldNameBFROM tableName;
The order in which you list the attributes will be the order the attributes are displayed.
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SELECT flname, ffname FROM faculty;
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SELECT ffname, flname FROM faculty;
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Select Distinct
SELECT sclass FROM student;
SC--SRSRJRSOSOFR
SELECT DISTINCT sclass FROM student;
SC--SRJRSOFR
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Filtering Data: The WHERE Clause
SELECT fieldName FROM tableNameWHERE fieldName [some
condition];
Returns only those records that match the condition
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Example 1: Number
SELECT sfname, slname, fidFROM studentWHERE fid = 1;
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Example 2: String
SELECT sfname, slnameFROM studentWHERE sclass= 'SO';
RememberValues in strings are Case sensitive
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Comparison Operators …A and B - Intersect
A OR B –UNION: all of A (including
yellow, gray and purple) all of B
(including aqua, and purple and
gray)
C and B
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Logical Operators - OR
SELECT fieldNameA, fieldNameB FROM tableName WHERE attribute = X or attribute = Y;
Must match EITHER
Select client_fname, client_lname, add1, city, state, zip
From vet_clientWhere state = ‘NJ’ OR state = ‘PA’ ;
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Arithmetic Operators – Rules of Precedence
Arithmetic operators and rules of precedence
Table 5.5
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Logical Operators – AND SELECT fieldNameA, fieldNameB FROM tableName WHERE attribute = X AND attribute = Y;
Must match BOTH
Select client_fname, client_lname, add1, city, state, zip
From vet_clientWhere state = ‘NJ’ AND state= ‘PA’ ;
Would this work?
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Logical Operators – AND
Select client_fname, client_lname, add1, city, state, zip
From vet_clientWhere city= ‘Philadelphia’ AND state=
‘PA’ ;
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Comparison Operators
Symbol Description> Greater Than>= Greater than or equal to< Less Than<= Less than or equal to!=, <> Not equal toIN Looks for records with a value which is
equal to one of the values in a listBETWEEN Looks for records with a value between
two different values
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SELECT appt_date, appt_type, temperatureFROM vet_apptWHERE (temperature >= 102 ;
SELECT appt_date, appt_type,temperatureFROM vet_apptWHERE appt_type in (1, 2, 3)’
EXAMPLES of Comparison Operator
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Logical Operators – AND
SELECT fieldNameA, fieldNameB FROM tableName WHERE criteria
Select client_fname, client_lname, add1, city, state, zip
From vet_clientWhere state = ‘NJ’ AND fieldNameA = ‘PA’ ;
Would this work?
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Wildcard Characters
_ : 1 character %: multiple characters
SELECT client_lnameFROM vet_client
WHERE client_lname LIKE ‘_emple’;
SELECT client_lnameFROM vet_client
WHERE client_lname LIKE ‘%d%
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NULL/NOT NULL Operator
SELECT student_fname, student_lname,
FROM student WHERE student_mname IS NULL
SELECT student_fname, student_lname,
FROM student WHERE student_mname IS NOT NULL
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Sorting the Output: ORDER BY
SELECT client_lname, client_fnameORDER BY client_lname desc;
Can Nest orderASC is default
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Example:
SELECT bldg_code, room, capacityFROM location WHERE capacity >= 40ORDER BY capacity DESC, bldg_code ASC ;
BLDG_CODE ROOM CAPACITY--------------------------------------------------------SP 101 150BUS 211 55BUS 105 42SP 202 40
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To Summarize
SELECT (distinct)fieldName/s
FROM tableName
WHERE fieldName [some condition]
ORDER BY fieldName ASC/DESC;