SQL: Advanced Constructs

Size: px

Start display at page:

Download "SQL: Advanced Constructs"

Adele Terry
5 years ago
Views:

1 B0B36DBS, BD6B36DBS: Database Systems h p:// Prac cal Class 8 SQL: Advanced Constructs Author: Mar n Svoboda, mar n.svoboda@fel.cvut.cz Tutors: J. Ahmad, R. Černoch, M. Řimnáč, M. Svoboda, G. Šourek Czech Technical University in Prague, Faculty of Electrical Engineering

2 Database Schema Assume we have the following schema of a rela onal database for a simple bank informa on system CREATE TABLE accounts ( ida INT PRIMARY KEY, number VARCHAR(22) NOT NULL UNIQUE, owner VARCHAR(100) NOT NULL, city VARCHAR(50) NOT NULL, balance DECIMAL(15, 2) NOT NULL DEFAULT 0 ); CREATE TABLE transfers ( idt BIGINT PRIMARY KEY, date me TIMESTAMP NOT NULL, source INT REFERENCES accounts (ida) ON DELETE SET NULL, target INT REFERENCES accounts (ida) ON DELETE SET NULL, amount DECIMAL(15, 2) NOT NULL ); B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

3 Inser ons INSERT statement INSERT INTO table name ( column name ), VALUES ( expression ),, SELECT statement B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

4 Exercise 1 Insert two new bank accounts into our database Account 501 Number: /1111 Owner: Mar n Svoboda City: Liberec Account 502 Number: /1111 Owner: Irena Mlynkova City: Praha Use only one insert statement B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

5 Updates UPDATE statement UPDATE table name SET column name = expression DEFAULT, WHERE expression B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

6 Exercise 2 Update details of a par cular bank account Change a ributes of an account with iden fier 502 New owner: Irena Holubova New city: Praha Add interests to selected accounts Only owners from Liberec will be rewarded Interest rate equals to 1% B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

7 Dele ons DELETE statement DELETE FROM table name WHERE expression B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

8 Exercise 3 Remove a par cular bank account Delete a bank account with number /1111 What will be the impact on the following snippet of data? ida number owner city balance /1111 Mar n Svoboda Liberec /1111 Irena Holubova Praha idt date me source target amount :30: :45: Remove all bank accounts B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

9 Sample Data Assume we have the following sample data in our database INSERT INTO accounts VALUES (501, ' /1111', 'Mar n Svoboda', 'Liberec', ), (502, ' /1111', 'Irena Holubova', 'Praha', ), (503, ' /1111', 'Jiri Helmich', 'Liberec', ), (504, ' /1111', 'Mar n Necasky', 'Jicin', ), (505, ' /1111', 'Marek Polak', 'Praha', ); INSERT INTO transfers VALUES ( , ' :30:00', 501, 502, ), ( , ' :40:00', 502, 503, ), ( , ' :50:00', 503, 504, ), ( , ' :00:00', 503, 505, ), ( , ' :10:00', 501, 502, ), ( , ' :20:00', 501, 504, ); B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

10 Views CREATE VIEW statement CREATE VIEW view name ( column name ), AS SELECT statement WITH LOCAL CHECK OPTION CASCADED Op ons CASCADED is the default for CHECK OPTION B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

11 Exercise 4 Create a view on a table of accounts Select all accounts such that their owners are from Liberec their current balance is at least Preserve all the original columns B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

12 Exercise 5 A empt to insert two new bank accounts into the previous view Account 506 Number: /1111 Owner: Jakub Klimek City: Liberec Balance: 5000 Account 507 Number: /1111 Owner: Jakub Lokoc City: Brno Balance: Consider different view updateability op ons B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

13 Evalua on Plans EXPLAIN statement EXPLAIN ANALYZE VERBOSE statement Op ons ANALYZE Executes a given statement and shows actual run mes and other sta s cs VERBOSE Displays addi onal informa on regarding the evalua on plan B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

14 Exercise 6 Express the following select query Bank accounts of clients from Liberec with current balance below the overall average Include all the original columns, calculate the overall number of outgoing transfers for each such account Analyze the query evalua on plan B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

15 Index Structures CREATE INDEX statement CREATE INDEX index name ON table name ( column name ( expression ) ASC DESC ), B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

16 Exercise 7 Create an index on a table of accounts Construct this index such that it helps us with the effec ve evalua on of the previous query Analyze the query evalua on plan once again B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

17 Stored Procedures CREATE FUNCTION statement CREATE FUNCTION function name ( arg name arg type = expression ), RETURNS return type AS $$ definition $$ LANGUAGE sql ' definition ' plpgsql... Arguments accessible via,, when not named explicitly B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

18 Exercise 8 Create a stored procedure for bank transfers Input Transfer iden fier Source / target accounts Amount Ac ons Both accounts will be tested for their existence Sufficient balance of the source account will be checked Balances of both the accounts will be updated The transfer will be logged into the table of transfers The current me will be used as a transfer mestamp Execute this procedure for a sample transfer B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

19 Transac ons BEGIN, COMMIT, and ROLLBACK commands BEGIN TRANSACTION ISOLATION LEVEL READ UNCOMMITTED READ COMMITTED REPEATABLE READ SERIALIZABLE COMMIT TRANSACTION ROLLBACK TRANSACTION By default, individual statements are executed in autocommit mode unless encapsulated by an explicit transac on B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

20 Transac ons Isola on levels READ UNCOMMITTED The lowest isola on level Treated as READ COMMITTED in PostgreSQL READ COMMITTED Only rows commi ed before a given statement can be seen The default isola on level in PostgreSQL REPEATABLE READ Only rows commi ed before the first statement can be seen SERIALIZABLE Execu on of transac ons is guaranteed to be serializable The highest isola on level B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

21 Exercise 9 Execute the previous procedure as a transac on I.e. encapsulate its call into a transac on Choose an appropriate isola on level B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

22 Triggers CREATE TRIGGER statement CREATE TRIGGER trigger name BEFORE INSERT AFTER UPDATE DELETE OR ON table name FOR EACH STATEMENT ROW EXECUTE PROCEDURE function name ( arguments ) Op ons FOR EACH STATEMENT is the default mode B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

23 Exercise 10 Create a new trigger that allows us to check validity of account balances Invoke this trigger in a way that you will be able to check the impact of all and opera ons Access old / new values via / records B0B36DBS, BD6B36DBS: Database Systems Prac cal Class 8: SQL: Advanced Constructs

SQL: DML and Advanced Constructs Insert, Update, Delete, View, Index, Procedure, Transaction, Trigger

Courses B0B36DBS, A7B36DBS: Database Systems Practical Class 08: SQL: DML and Advanced Constructs Insert, Update, Delete, View, Index, Procedure, Transaction, Trigger Martin Svoboda 11. 4. 2017 Faculty