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SQL Data Modification

SQL Data Modification. Spread throughout chapter 7. Changing 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. Insert New Records.

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SQL Data Modification

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  1. SQL Data Modification • Spread throughout chapter 7

  2. Changing 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

  3. Insert New Records • Simplest form - single record INSERT INTO enrollments VALUES (‘66419’,’2121’,’’,’’);

  4. Insert 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’);

  5. Inserting • 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

  6. Inserting 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);

  7. 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;

  8. DELETE • 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;

  9. UPDATE • 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’;

  10. 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’;

  11. Basic Data Management • Saving the Table Contents COMMIT <table names>; COMMIT PRODUCT; • Restoring the Table Contents ROLLBACK

  12. End Updates – and Thus End DML

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