Table Alteration. Reminder. Altering Tables (cont.) Altering Tables. Altering Tables (cont.) We have covered: Today we ll t alk about :

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1 Reminder We have covered: Creating tables Converting ER diagrams to table definitions Today we ll t alk about : Altering tables Inserting and deleting data from tables Querying tables Table Alteration Altering Tables Table definitions can be altered after their creation Adding columns Changing columns def init ion Dropping columns Adding or dropping constraints And mor e Use the reserved word ALTER Altering Tables (cont.) Adding a column: ALTER TABLE Employee ADD ( Mname VARCHAR2(20), Birthday DATE ); Changing columns definition: ALTER TABLE Emplyee Modify ( Mname VARCHAR2() ); Cannot be NOT NULL unless the table is empty Altering Tables (cont.) Dropping columns: ALTER TABLE Employee DROP COLUMN Mname; Dropping multiple columns: ALTER TABLE Employee DROP (Mname, Birthday); Adding constraints: ALTER TABLE Department ADD( FOREIGN KEY (ManrId) REFERENCES Employee(SSN)); Inserting, deleting, and updating data in a table

2 The Employee Table > Describe Employee Name Null? Type SSN FNAME LNAME GENDER NUMBER VARCHAR2(20) VARCHAR2(20) CHAR(1) SALARY NOT NULL NUMBER(5) Inserting a Row To insert a row into the Employee table: INSERT INTO Employee(SSN, Fname, Lname, Salary) VALUES(121, Sara, Cohen,000); The remaining columns get default values (or NULL) When will this fail? Some More Det ails The f ields don t have t o be specif ied if values are specified for all columns and in the order defined by the table Example: INSERT INTO Employee VALUES(121, Sara, Cohen, `F, 00); General format: Deleting Rows DELETE FROM Table WHERE Cond; Deletes all rows satisfying Cond from Table For example, to remove the employee with SSN 121 from the Employee table: DELETE FROM Employee WHERE SSN = 121; Deleting Rows (cont.) To remove all male employees having a salary greater than 150,000 shekels: DELETE FROM Employee WHERE Salary > ; Updating Rows We can update rows in a table General format: UPDATE Table SET Field1=value1,,,FieldN=valueN WHERE Cond Now we can reduce salaries instead of firing employees: UPDATE Employee SET Salary = WHERE Salary > ;

3 The ORACLE Bulk Loader A tool that provides easy insertion of large amounts of rows into tables. The idea: the values of the inserted rows are kept in a compact file: the Data file. We define the structure of the Data file, in the Control file. mydata.dat Here we enter the data we want to insert (employees) myctrl.ctl Here we specify the structure of the data file The Control File For example, we can load 3 employees from the file myemp.dat that contains the following lines: Shaquile Oneil 121 Magic Johnson 134 Doron Sheffer 156 A simple control file: LOAD DATA INFILE <datafile> [APPEND] INTO TABLE <tablename> FIELDS TERMINATED BY '<separator> (<list of all attribute names to load>) The Control File (cont.) <datafile>: The name of the data file <tablename>: The name of the table into which the data will be loaded (appended if APPEND is specified, or else the table must be empty) <separator>: A string that separates two field values of a row The attributes are separated by commas and enclosed in parentheses Example: The Control File (cont.) mycontrol.ctl LOAD DATA INFILE myemployees.dat INTO TABLE Employees FIELDS TERMINATED BY ' ' ( Fname, Lname, SSN) myemployees.dat Moshe Cohen 334 Miri Levi 99 Alon Hazan 99 When the control file is run, this will insert the 3 employees into the employees table The attributes that are unspecified will be set to NULL (or default values if they are specified) The Data File The Bulk Loader coners every single line to represent one row in the table Even an empty line! (which will usually result in an error) Spaces are not ignored in the data file! thus the rows sara cohen 121 and sara cohen 121 define different functionalities The NULL value is implied by the NULL keyword or the empty string The Data File (continued) The control and the data files can be combined into one.ctl file using the following format: LOAD DATA INFILE * INTO TABLE Employees FIELDS TERMINATED BY ' ' (Fname, Lname, SSN) BEGINDATA Sara Cohen 121 Benny Kimelfeld 134 Yaron Kanza 156

4 The Bulk Invocation To invoke the bulk loader, issue the following command directly from the Unix shell: Sqlldr <ctrlfilename> Erroneous lines in the data file are ignored and written into <ctrlfilename>.bad, and any other relevant information is written into <ctrlfilename>.log. SQL Queries The tables you fill using the Bulk Loader should be created prior to the loader invocation Before invoking the Bulk Loader you have to make sure that no SqlPlus sessions are open. Query Components A query can contain the following clauses select from where group by having order by Only select and from are required Order of clauses is always as above Very Basic SQL Query SELECT [Distinct] Attributes FROM relation Attributes: A list of attributes onto which the query projects (For example: Eid, Ename). Relation: A relation to perform the query on. DISTINCT: Optional keyword to delete duplicates Example: Select studentid, studentname From students StudentID 1123 StudentDept. Math StudentName Moshe StudentAge 25 Basic SQL Query Result: Computers Mickey 26 Math Menahem 29 Select studentid, studentname From students StudentID StudentName 1123 Moshe 45 Mickey Menahem SELECT [Distinct] Attributes FROM relation WHERE condition Attributes: A list of fields onto which the query projects (For example: Eid, Ename). relation: A relation to perform the query on condition: A Boolean condition (For example: Eid>21, or Ename=Yuval ) DISTINCT: Optional keyword to delete duplicates

5 StudentID 1123 StudentDept. Math StudentName Moshe StudentAge 25 Basic SQL Query 45 Computers Mickey Math Menahem Select studentid, studentname From students 29 SELECT [Distinct] attributes FROM relation WHERE condition; Result: Where StudentDept= Math StudentID StudentName 1123 Moshe Notice! The "SELECT" clause defines the operation of projection from the relational model. Selection is defined by the WHERE clause Menahem SQL and relational algebra Basic SQL Query SELECT Distinct A 1,,A n FROM R 1,,R m WHERE C; SELECT [Distinct] Attributes FROM relationslist WHERE condition relationslist: A list of relations. The query is performed on the product of these relations (AxBxC ). A 1,,A n ( C (R 1 x x R m )) Basic SQL Query Example Tables Used SELECT [Distinct] attributes FROM relations WHERE condition; Important! The evaluation order is: sname rating bid Boats bname color Nancy red Gloria green 1. Compute the cross product of the tables in relations. 2. Delete all rows that do not satisfy condition. 3. Delete all columns that do not appear in attributes. 4. If Distinct is specified eliminate duplicate rows. bid day

6 What does this compute? St 1: x Select sname from sailors, reserves Where sailors.= reserves. sname rating bid day sname rating bid day St 2: where sailors.=reserves. St 2: where sailors.=reserves. sname rating bid day sname rating bid day St 3: select sname St 3: select sname sname rating bid day sname Final answer

7 Example Query SELECT DISTINCT sname, FROM WHERE rating>; Q: What does this compute? A: Distinct names and s of sailors with rating >. Q: Write it in algebra Example Query SELECT DISTINCT sname FROM, WHERE. =. and bid = ; Q: What does this compute? A: names of sailors who reserved boat Q: Write it in relational algebra A: sname, ( rating>()) sname (. =. ( x )) bid =. =. bid = sname x sname rating bid day sname rating bid day Range Variables Example Query FROM S, R WHERE S. = R. and R.bid = ; Range variables are good style. They are necessary if the same relation appears twice in the FROM clause Similar to Renaming in Relational Algebra FROM S, R WHERE S. = R. and R.bid!= ; Q: What does this return? A: Names of sailors who reserved a boat other than boat Notice: sailors who reserved both boat and a different boat will appear!

8 A Few SELECT Options Select all columns: SELECT * FROM ; Rename selected columns: AS _Name FROM S; Applying functions (e.g., Mathematical manipulations) SELECT (- 5)*2 FROM S; Select operators The aggregate operators available in SQL are: COUNT(*) COUNT([DISTINCT] A) SUM([DISTINCT] A) AVG([DISTINCT] A) MAX(A) MIN(A) NULL values are ignored SELECT Max(S.) FROM S Examples SELECT count(distinct S.) FROM S, R WHERE S. = R. SELECT Avg(S.) FROM S, R WHERE S. = R. and R.bid=112 The WHERE Clause Numerical and string comparison:!=,<>,=, <, >, >=, <=, between(val1 AND val2) Logical components: AND, OR Null verification: IS NULL, IS NOT NULL Checking against a list with IN, NOT IN. SELECT sname FROM Examples WHERE >=40 AND rating IS NOT NULL ; SELECT, sname FROM sailors WHERE IN (13, 2334, 3344) or sname bet ween( Geor ge and Paul ); User s Table List ORACLE holds tables with some general information about the tables in your database Such Tables are: Cat, user_objects To see the list of all your tables print: SELECT * FROM Cat; To see the list of all your objects print: SELECT object_name, timestamp, object_type FROM user_objects;

9 The LIKE Operator A pattern matching operator (regular expression) Basic format: colname LIKE pattern Example: SELECT FROM WHERE sname LIKE R_%y ; _ is a single character % is 0 or more characters SQL query SELECT S. FROM S, R WHERE S. = R.; When would adding DISTINCT give a different result? Are any of these the same? SELECT S. FROM S, R WHERE S. = R.; SELECT DISTINCT R. FROM S, R WHERE S. = R.; SELECT R. FROM R sname rating bid day Example Query How would you query sailors who have reserved more than one boat? FROM S, R1, R2. WHERE S. = R1. and R1.=R2. and R1.bid!=R2.bid; SQL query FROM S, R, Boats B WHERE S. = R. and R.bid = B.bid and B.color = 'red' Q: What does this return? A: Names of sailors who have reserved a red boat. SQL query Q: How would you query the colors of boats reserved by Bob? A: SELECT distinct B.color FROM S, R, Boats B WHERE S.sname = Bob and S. = R. and R.bid = B.bid

10 Order Of the Result The ORDER BY clause can be used to sort results by one or more columns The default sorting is in ascending order Can specify ASC or DESC Example SELECT sname, rating, FROM S WHERE > 50 ORDER BY rating ASC, DESC Other Relational Algebra Operators So far, we have seen selection, projection and Cartesian product How do we do operators UNION and MINUS? Three SET Operators [Query] UNION [Query] [Query] MINUS [Query] [Query] INTERSECT [QUERY] Note: The operators remove duplicates by default! How would you express intersect in Relational Algebra? What does this return? SELECT DISTINCT S.sname FROM S, R, Boats B WHERE S. = R. and R.bid = B.bid and (B.color = 'red' or B.color='green') What would happen if we replaced or by and? Then how can we query sailors who have reserved both a green and a red boat? who ve reserved red or green boat FROM S, Boats B, R WHERE S. = R. and R.bid = B.bid and B.color = red UNION Would INTERSECT here give us sailors who reserved both red and green boats? FROM S, Boats B, R WHERE S. = R. and R.bid = B.bid and B.color = green ;

11 who ve reserved red and green boats Multiset (Bag) Operators Union without removing duplicates: UNION ALL FROM S, R1, R2 Boats B1, Boats B2 WHERE S. = R1. and R1.bid = B1.bid and B1.color = red and S. = R2. and R2.bid = B2.bid and B2.color = green ; SELECT FROM UNION ALL SELECT FROM DISTINCT sname S DISTINCT sname S Nested queries in WHERE Nested Queries Equality nested query: Select R.bid From S, R Where = (select from S where sname=geor ge ); When would t his wor k? When wouldn t it? Nested queries in WHERE Subqueries with multiple results: FROM S WHERE S. IN (SELECT R. FROM R WHERE R.bid = ); Names of sailors who ve reserved boat What would happen if we wrote NOT IN? What does this produce? FROM S WHERE S. NOT IN (SELECT R. FROM R WHERE R.bid IN (SELECT B.bid FROM Boats B WHERE B.color='red'))

12 Set- Comparison Queries who are not the youngest: SELECT * FROM S1 WHERE S1. > ANY (SELECT S2. FROM S2); We can also use op ALL (op is >, <, =, >=, <=, or <>). Correlated Nested Queries Names of sailors who ve reserved boat : SELECT S. What would happen if FROM S we wrote NOT EXISTS? WHERE EXISTS (SELECT * FROM R WHERE R.bid = and S. = R.); S not in subquery, refers to outer loop Exists and Not Exists Differs from In and Not In by not matching attributes. Exists: For every tuple in the outer loop, the inner loop is tested. If the inner loop produces a result, the outer tuple is added to the result.

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