1 SQL - introduction. Lecture Agenda. SQL - introduction. Language elements. Queries. Data modification. Transaction control.

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1 Lecture Agenda SQL - introduction Language elements Queries Data modification Transaction control 1 SQL - introduction SQL history SQL - Structured Query Language SEQUEL (Structured English QUEry Language)was developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1970s, it was designed to manipulate and retrieve data stored in IBM s original quasi-relational database management system, System R. In the late 1970s, Relational Software, Inc. (now Oracle Corporation) developed their own SQL-based RDBMS with aspirations of selling it to the U.S. Navy, Central Intelligence Agency, and other U.S. government agencies. In June 1979, Relational Software, Inc. introduced the first commercially available implementation of SQL, Oracle V2 (Version2) for VAX computers. SQL was adopted as a standard by the American National Standards Institute (AN- SI) in 1986 as SQL-86[35] and the International Organization for Standardization (ISO) in SQL features declarative language interpreted language data sublanguage access to data from the relation level similar to the natural language uses a trivalent logic uses relational algebra is not entirely consistent with the relational model 1

2 SQL - capabilities SQL allows to: issuing queries insert, delete and modify data create databases create, modify, and delete relational objects manage transactions manage databases SQL forms SQL interactive Static SQL Embedded SQL Modular Dynamic SQL SQL parts DML (Data Manipulation Language): SELECT, UPDATE, INSERT, DELETE; DDL (Data Definition Language): CREATE, DROP, ALTER; DCL (Data Control Language): GRANT, REVOKE, COMMIT, ROLLBACK itp.). SQL cons Most implementors do not support the entire standard. SQL deviates in several ways from its theoretical foundation, the relational model and its tuple calculus. Many database vendors have large existing customer bases; where the newer version of the SQL standard conflicts with the prior behavior of the vendor s database, the vendor may be unwilling to break backward compatibility. The standard does not specify database behavior in several important areas (e.g. indexes, file storage...), leaving implementations to decide how to behave. 2

3 2 Language elements SQL Statement Several of the SQL language elements that compose a single statement: Clauses, which are constituent components of statements and queries. (In some cases, these are optional.) Expressions, which can produce either scalar values, or tables consisting of columns and rows of data. Predicates, which specify conditions that can be evaluated to SQL three-valued logic (3VL) (true/false/unknown) or Boolean truth values and are used to limit the effects of statements and queries, or to change program flow. Queries, which retrieve the data based on specific criteria. This is an important element of SQL. Statements, which may have a persistent effect on schemata and data, or may control transactions, program flow, connections, sessions, or diagnostics (SQL statements also include the semicolon ( ; ) statement terminator). Basic SQL ANSI data types CHARACTER(n), CHAR(n) CHARACTER VARYING(n), CHAR VARYING(n) NUMERIC(p,s), DECIMAL(p,s) INTEGER, INT, SMALLINT FLOAT(b), DOUBLE PRECISION, REAL DATE: YYYY-MM-DD TIME: HH:MM:SS.p TIMESTAMP: YYYY-MM-DD HH:MM:SS.p INTERVAL BLOB CLOB XML Aliases of data types SQL ANSI Oracle DB2 MySQL PostgrSQL MS SQL CHARACTER(n) CHAR(n) CHARACTER(n) CHAR(n) CHAR(n) CHAR(n) CHAR(n) CHARACTER VARCHAR2(n) VARCHAR(n) VARCHAR(n) VARCHAR(n) VARCHAR(n) VARYING(n) CHAR VARYING(n) NUMERIC(p,s) NUMBER(p,s) DECIMAL(p,s) DECIMAL(p,s) NUMERIC(p,s) DECIMAL(p,s) DECIMAL(p,s) INTEGER NUMBER(38) INTEGER INT, INTEGER INT, INTEGER INTEGER INT, SMALLINT SMALLINT FLOAT(b) NUMBER(p,s) FLOAT(b) FLOAT(b) NUMERIC(p,s) FLOAT(b) DOUBLE PRECISION REAL DATE DATE DATE DATE DATE DATETIME TIME DATE TIME TIME TIME DATETIME TIMESTAMP TIMESTAMP TIMESTAMP TIMESTAMP TIMESTAMP DATETIME INTERVAL INTERVAL - +- INTERVAL - BLOB BLOB BLOB BLOB BYTEA VARBINARY(n) CLOB CLOB CLOB TEXT TEXT TEXT XML XMLTYPE XML +- XML +- 3

4 Literals chains in single quotes text date, time and timestamps saved as text literals in single quotes; require the format: YYYY-MM-DD HH:MM:SS.p, np :23:34.45 numbers: 12, 45e-2 Intervals An interval literal specifies a period of time. You can specify these differences in terms of years and months, or in terms of days, hours, minutes, and seconds. INTERVAL 3-5 YEAR TO MONTH INTERVAL 5 YEAR INTERVAL 5 10:12 DAY TO MINUTE Datetime arithmetic in SQL Typ Operator Type Result DATE/TIMESTAMP + - NUMERIC DATE DATE/TIMESTAMP + - INTERVAL DATE/TIMESTAMP INTERVAL + DATE/TIMESTAMP DATE/TIMESTAMP TIMESTAMP + - DATE/TIMESTAMP INTERVAL DATE - DATE INTERVAL (in Oracle NUMBER - number of days) INTERVAL + - INTERVAL INTERVAL INTERVAL * / NUMERIC INTERVAL NUMERIC * INTERVAL INTERVAL Operatory arithmetic operator (+, -,*,/) comparison operators ( =, <>, <, <=, >, >=, LIKE, NOT LIKE) between an inclusive range operator BETWEEN equal to one of multiple possible values IN concatenation operator logic (ALL, AND, ANY, EXISTS, NOT, OR ) set operators (UNION, INTERSECT, EXCEPT (MINUS w Oracle)) unary operators (+, -) Compare to NULL IS, IS NOT The hierarchy of operators ( ) +, - (unary operators) *, / +, - =, >, <, >=, <=, <> 4

5 NOT AND ALL, ANY, BETWEEN, IN, LIKE, OR, SOME = (assignment) Expressions attributes (last_name, salary) pseudocolumns (CURRVAL, NEXTVAL, LEVEL, ROWID, ROWNUM) numbers (20, 16, , itp.) chains ( Kowalski, Dyrektor, itp.) arithmetic (placa+dod_funkcyjny, placa*12, 5/6, itp.) concatenation (imie nazwisko, itp.) functions relations 3 Queries Conventions UPPERCASE - SQL keywords lower case - user defined elements [] - optional elements {} - optional elements, one of which is mandatory - character separating the options Query SELECT [DISTINCT] list_of_expressions FROM list_of_realtions [WHERE conditions] [GROUP BY criteria [HAVING conditions]] [ORDER BY criteria [DESC]]; SELECT and FROM are mandatory the order of the clauses can not be changed 5

6 SELECT SELECT defines what columns will be included in the resulting relation (defines the attributes of projection); keyword DISTINCT remove duplicates; operator * means all of the attributes of the input relation. There is a possibility of using aliases (nicknames) for expressions: SELECT first_name last_name ; SELECT first_name last_name ; SELECT first_name last_name ; employee AS employee AS "employee data" FROM and WHERE FROM specifies the input relations, from which data will be collected; the names of the tables can be given aliases. WHERE defines the conditions that must be satisfied by the rows of the resulting relation (implementation of restrictions). SELECT first_name, last_name, job_id, department_id WHERE (department_id = 80 OR department_id = 40) AND job_id LIKE %REP ; GROUP BY GROUP BY enables division of relations into subsets - aggregation. Single subset / group consists of rows for which the grouping criterion has the same value. After the SELECT can occur only those expressions that are the subject of the action clause GROUP BY, and the arguments of aggregate functions. SELECT department_id, Count(last_name) GROUP BY department_id; SELECT department_id, job_id, Count(last_name) GROUP BY department_id, job_id; HAVING HAVING defines the conditions that must be satisfied by a subset to be included in the result; conditions in WHERE refers to relation before aggregation, HAVING - after). 6

7 SELECT department_id, Count(last_name) GROUP BY department_id HAVING Count(last_name) > 30; ORDER BY ORDER BY enables sorting of the resulting data. Sorting criterion can be input attribute of relations, alias, or number in the list of SELECT. Reverse the order of sorting is obtained by adding the keyword DESC. SELECT last_name employee, job_id, department_id ORDER BY department_id, 2 DESC, employee; Set Operators Set operators combine the results of two component queries into a single result. Queries containing set operators are called compound queries. UNION - All distinct rows selected by either query UNION ALL - All rows selected by either query, including all duplicates INTERSECT - All distinct rows selected by both queries MINUS - All distinct rows selected by the first query but not the second SELECT job_id WHERE department_id = 40 MINUS SELECT job_id WHERE department_id = 80; Joins A join is a query that combines rows from two or more tables, views, or materialized views. Most join queries contain at least one join condition, either in the FROM clause or in the WHERE clause. The join condition compares two columns, each from a different table. FROM tab1 [AS alias] {CROSS JOIN { [NATURAL] [join_type] JOIN tab2 [AS alias] { ON cond1 [{AND OR} cond2] [...] ] USING (atr1 [,...]) } } Types of joins We have few types of joins Cartesian Product natural join θ-join outer join self join 7

8 Cartesian Product Cross Join If two tables in a join query have no join condition, then query returns their Cartesian product. Result is a combination of each row of one table with each row of the other. A Cartesian product always generates many rows and is rarely useful. SELECT * CROSS JOIN departments; rows selected Conditional join θ-join results in a Cartesian product, limited to those tuples for which the condition θ was met. An equijoin is a join with a join condition containing an equality operator. An equijoin combines rows that have equivalent values for the specified columns. SELECT * e JOIN departments d ON (e.department_id = d.department_id); SELECT * e JOIN departments d USING(department_id); Natural join A Natural Join is a JOIN operation that creates an implicit join clause for you based on the common columns in the two tables being joined. Common columns are columns that have the same name in both tables. SELECT * NATURAL JOIN departments; Outer Join Outer Join An outer join extends the result of a simple join. An outer join returns all rows that satisfy the join condition and also returns some or all of those rows from one table for which no rows from the other satisfy the join condition. Types of outer joins: left right full SELECT * e LEFT JOIN departments d ON (e.department_id = d.department_id); 8

9 Self join Self join is a join of a table to itself. SELECT e.last_name employee, ch.last_name chief e JOIN employees ch ON (e.manager_id = ch.employee_id); Subquery A subquery is a SQL query nested inside onother query. A subquery may occur in a SELECT, FROM, WHERE and HAVING clause. A subquery must be enclosed in parentheses Types of subqueries: simple - the inner query executes first before its parent query so that the results of inner query can be passed to the outer query. SELECT last_name, salary, job_id, department_id WHERE salary = (SELECT Min(salary) ); corelated subquery(also known as a synchronized subquery) - reference one or more columns in the outer SQL statement. The subquery is evaluated once for each row processed by the outer query. SELECT Last_name, salary, job_id, department_id e WHERE salary = (SELECT MAX(salary) WHERE department_id = e.department_id); 4 DML - data modification UPDATE UPDATE is used to update tuples in a table. The WHERE clause specifies which tuple or tuples should be updated. If you omit the WHERE clause, all records will be updated! Składnia: UPDATE {table vie} SET {{attribute = value DEFAULT NULL}, {attribute = value DEFAULT NULL},...} [WHERE condition]; Examples: 9

10 UPDATE employees SET salary = salary * 1.1; UPDATE employees SET salary = salary * 1.1 WHERE employee_id IN (SELECT manager_id ); INSERT INSERT is used to insert new records in a table. Optionally, you can specify a list of supplemented attributes, if not, please complete all. Clause VALUES determine value that will be assigned to attribute. Tuple can be filled with values returned by the subquery. INSERT INTO {table view} [(attribute1 [,...] )] {DEFAULT VALUES VALUES (value1 [,...]) SELECT... }; Examples: INSERT INTO employees VALUES (9121, Mike, Wazowski, mike_monster@gmail.com, , To_date( 2014/04/02, yyyy/mm/dd ), HR_REP, 5000, NULL, 101, 40); INSERT INTO employees (employee_id, last_name, , hire_date, job_id) VALUES (9192, Wazowski, mike_monster@gmail.com, To_date( 2014/04/02, yyyy/mm/dd ), HR_REP ); INSERT INTO archives SELECT * WHERE employee_id=9192; DELETE DELETE removes existing rows from a table, the WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted! DELETE FROM {table view} [WHERE condition]; Przykłady: DELETE FROM jobs; DELETE WHERE employee_id = 9192; 10

11 5 TCL - transaction control COMMIT COMMIT - ends your current transaction and make permanent all changes performed in the transaction. A transaction is a sequence of SQL statements that database server treats as a single unit. This statement also erases all savepoints in the transaction and releases transaction locks. Oracle Database issues an implicit COMMIT before and after any data definition language (DDL) statement. A normal exit from most utilities and tools causes the current transaction to be committed. ROLLBACK ROLLBACK Use the ROLLBACK statement to undo work done in the current transaction or to manually undo the work done by an in-doubt distributed transaction. If you do not explicitly commit the transaction and the program terminates abnormally, then database server rolls back the last uncommitted transaction. Using ROLLBACK without the TO SAVEPOINT clause performs the following operations: Ends the transaction Undoes all changes in the current transaction Erases all savepoints in the transaction Releases any transaction locks Using ROLLBACK with the TO SAVEPOINT clause performs the following operations: Rolls back just the portion of the transaction after the savepoint. It does not end the transaction. Erases all savepoints created after that savepoint. The named savepoint is retained, so you can roll back to the same savepoint multiple times. Prior savepoints are also retained. Releases all table and row locks acquired since the savepoint. Other transactions that have requested access to rows locked after the savepoint must continue to wait until the transaction is committed or rolled back. Other transactions that have not already requested the rows can request and access the rows immediately. 6 Bibliography References M. Lentner, Oracle 9i Kompletny podręcznik użytkownika, PJWSTK - W-wa,