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SQL Data ModificationSQL Data Modification

Spread throughout chapter 7

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Changing a TableChanging a Table

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

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Insert New RecordsInsert New Records

Simplest form - single record

INSERT INTO enrollments

VALUES (‘66419’,’2121’,’’,’’);

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Insert New RecordsInsert New Records

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’);

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InsertingInserting

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

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Inserting from a QueryInserting from a Query

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);

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Inserting from a Query (con)Inserting from a Query (con) Then can fill table from query results:

INSERT INTO dept_info (dname, NUM_CLASSES, TOTAL_ENROLL, MAX_ENROLL)

SELECT DEPT, COUNT(*), SUM (enrollment), MAX (enrollment)

FROM SECTIONS

GROUP BY DEPT;

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DELETEDELETE

DELETE is pretty simple - it removes a set of records (generally that meet some condition)

DELETE

FROM STUDENT

WHERE SSN = ‘1111’;

DELETE

FROM STUDENT

WHERE GPA < 1.5;

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UPDATEUPDATE UPDATE can modify one or more attributes in one or

more records. WHERE clause selects records to be modified

UPDATE STUDENT

SET HOMETOWN = ‘Vorhees’

WHERE SSN = ‘1113’;

Can do multiple attributes:UPDATE SECTIONS

SET TIME = ‘MW610’, ROOM = ‘BC125’

WHERE INDEX = ‘66420’;

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UPDATE (con)UPDATE (con) Can modify multiple records:

UPDATE STUDENT

SET YEAR = ‘Sr’

WHERE numcreditsearned > 90;

Can modify using a calculation:UPDATE SECTIONS

SET STOP = STOP + 5

WHERE DEPT = ‘CSC’ AND COURSE = ‘157’;

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Basic Data ManagementBasic Data Management

Saving the Table ContentsCOMMIT <table names>;

COMMIT PRODUCT;

Restoring the Table ContentsROLLBACK

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End Updates – and Thus End DMLEnd Updates – and Thus End DML