Web app development_my_sql_09

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Web app development_my_sql_09

  1. 1. hasen@microcis.net July 16, 2013Hassen poreya Trainer, Cresco Solution Afghanistan Workforce Development Program Database MySQL, Modification Commands
  2. 2. Modification Commands  There are three SQL commands to modify the database:  INSERT  DELETE  UPDATE
  3. 3. INSERT Command  In its simplest form, it is used to add one or more tuples to a relation.  Tuples are the rows  Relations are the tables.  Attribute values should be listed in the same order as the attributes were specified in the CREATE TABLE command.
  4. 4. INSERT Command INSERT INTO table name VALUES (value1, value2, ...);  Values are separated by comma ,  Strings, Dates are enclosed by single quotation marks ‘’  Values have to be sorted according to the table structure (the columns)
  5. 5. INSERT Command INSERT INTO employee VALUES (1,'John',‘ Smith', 'Berlin', '1979- 09-04', 1000.40); INSERT INTO project VALUES (1, 'Database Design', 'Kabul'); INSERT INTO works in VALUES(1,1,40);
  6. 6. INSERT Command INSERT INTO employee VALUES (NULL, 'Anna', 'Conner', 'London', '1960-11-10‘,1.40); What will happen if we put null value in the id field?
  7. 7. INSERT Command  If we used AUTO INCREMENT for the definition of a column, the database system will automatically compute a unique value for Id.  The value is computed by incrementing the maximum value for Id already in the database.
  8. 8. DELETE Command  Removes tuples from a relation.  Includes a WHERE clause to select the tuples to be deleted.  A missing WHERE clause species that all tuples in the relation are to be deleted; the table then becomes an empty table.  The number of tuples deleted depends on the number of tuples in the relation that satisfy the WHERE clause.
  9. 9. DELETE Command DELETE FROM table name WHERE condition; DELETE FROM employee WHERE id=1; DELETE FROM project WHERE location=‘kabul’;
  10. 10. INSERT Command: Integrity Constraints  Integrity Constraints:  One of the tasks of a database system is to make (automatically) sure that the stored data is in a consistent state.  When we model the Mini-World we also model what a consistent state means for us by defining integrity constraints.  In our company each employee is assigned a unique id as the PRIMARY KEY
  11. 11. Integrity Constraints: PRIMARY KEY  Primary Key  Database system automatically rejects all new records with a key that is already stored in the database as below:
  12. 12. Integrity Constraints: UNIQUE  UNIQUE  Similar to primary key: has to be unique  We do not want to use name as a primary key to identify records, but still we want to express that it has to be unique.
  13. 13. Integrity Constraints: NOT NULL  NOT NULL  Sometimes we want to make sure that a value is always assigned to a column, so we use NOT NULL  Primary keys are automatically defined as NOT NULL (we couldn't identify an employee if there is no Id stored)
  14. 14. Modification Command: UPDATE  It is used to modify attribute values of one or more selected tuples.  A WHERE clause selects the tuples to be modified.  An additional SET clause species the attributes to be modified and their new values.
  15. 15. Modification Command: SELECT  Extract data stored in some columns of some table.  General syntax is: SELECT column name1, column name2, ... FROM table name; SELECT * FROM table name;  The asterisk (*) retrieves all attributes form the specified table.
  16. 16. Modification Command: SELECT SELECT last name, location, salary FROM employee
  17. 17. Modification Command: SELECT SELECT * FROM employee
  18. 18. SELECT Command: WHERE  Basic form of the SQL SELECT statement is called a mapping or a SELECT-FROM-WHERE- block. SELECT < attributelist > FROM < tablelist > WHERE < condition >  < condition > is a conditional (Boolean) expression that identifies the tuples to be retrieved by the query.
  19. 19. SELECT Command: WHERE SELECT location, salary FROM employee WHERE last_name=Smith;
  20. 20. SELECT Command: ORDER BY  Sort the result according to some column, descending or ascending.
  21. 21. SELECT Command: ORDER BY  Compare the result with the same query using ORDER BY.
  22. 22. Let’s do something
  23. 23. hasen@microcis.net July 16, 2013Hassen poreya Trainer, Cresco Solution Any Questions!

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