SQL Data Modification
 Spread throughout chapter 7
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Changing a Table
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 While there is One SQL statement to obtain
info (SELECT), there are 3 for changing a
table



INSERT - adds records to a table
DELETE - deletes records from a table
UPDATE - changes records in a table
Insert New Records
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 Simplest form - single record
INSERT INTO enrollments
VALUES (‘66419’,’2121’,’’,’’);
Insert New Records
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 single record - perhaps not all attributes
INSERT INTO enrollments(stdssn , classindex)
VALUES (‘1113’,’66419’);
 We can insert more than one record at a time
INSERT INTO enrollments(classindex,stdssn)
VALUES (‘66416’,’1111’), (‘66416’,’2222’);
Inserting
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 DBMS should enforce all constraints - including
referential integrity, no value for attribute specified as
NOT NULL, duplicate primary key values
 All DBMSs may not fully enforce - then user and/or
programmer must defend against errors
Inserting from a Query
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 Since the result of a query is a table, we can actually
load data into a (usually temporary) table as a result of a
query
 First need to create table – not covered yet – here’s a
simple table creation:
CREATE TABLE dept_info (dname CHAR (3),
NUM_CLASSES INTEGER,
TOTAL_ENROLL INTEGER,
MAX_ENROLL INTEGER);
Inserting from a Query (con)
 Then can fill table from query results:
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INSERT INTO dept_info (dname, NUM_CLASSES,
TOTAL_ENROLL, MAX_ENROLL)
SELECT DEPT, COUNT(*), SUM (enrollment), MAX (enrollment)
FROM SECTIONS
GROUP BY DEPT;
DELETE
 DELETE is pretty simple - it removes a set of records
(generally that meet some condition)
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DELETE
FROM STUDENT
WHERE SSN = ‘1111’;
DELETE
FROM STUDENT
WHERE GPA < 1.5;
UPDATE
 UPDATE can modify one or more attributes in one or
more records.
 WHERE clause selects records to be modified
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UPDATE STUDENT
SET HOMETOWN = ‘Vorhees’
WHERE SSN = ‘1113’;
 Can do multiple attributes:
UPDATE SECTIONS
SET TIME = ‘MW610’, ROOM = ‘BC125’
WHERE INDEX = ‘66420’;
UPDATE (con)
 Can modify multiple records:
UPDATE STUDENT
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SET YEAR = ‘Sr’
WHERE numcreditsearned > 90;
 Can modify using a calculation:
UPDATE SECTIONS
SET STOP = STOP + 5
WHERE DEPT = ‘CSC’ AND COURSE = ‘157’;
Basic Data Management
 Saving the Table Contents
COMMIT <table names>;
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COMMIT PRODUCT;
 Restoring the Table Contents
ROLLBACK
End Updates – and Thus End DML
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