2 PL/SQL - fundamentals Variables and Constants Operators SQL in PL/SQL Control structures... 7

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1 Table of Contents Spis treści 1 Introduction 1 2 PLSQL - fundamentals Variables and Constants Operators SQL in PLSQL Control structures Summary 10 4 Resources 10 1 Introduction PLSQL PLSQL (ang. Procedural LanguageStructured Query Language) - procedural extension of SQL (based on the ADA language). Allows the use of structures such as loops, conditional statements, variables, and creating procedures, functions, triggers, supporting the concrete implementation of the database. It was developed by Oracle Corporation in the early 90 s to enhance the capabilities of SQL (each distributor provides its solutions (eg. PLpgSQL in PostgreSQL), which are similar to the PLSQL). Features PLSQL procedural language oriented on data processing a compiled language supports variables, constants, control structures, exceptions has a block structure each statement within a block of PL SQL is followed by a semicolon ; assignment operator is :=, can contain DML and TCL instructions can not contain DDL and DCL (session control) provides reusable program units 1

2 2 PLSQL - fundamentals PLSQL blocks The basic unit PLSQL is a block, we have: anonymous blocks, named blocks, subprograms. A PLSQL block consist of four sections: declarative (optional), executable section that starts with begin (required), exceptional handling (optional), ebd; (mandatory) PLSQL block structure [ variables; cursors; user_defined_exceptions;] SQL_statements; PLSQL_statements; [EXCEPTION exception_handling;] Comments There are two syntaxes that you can use to create a comment: a single line: -- many lines: starts with *, ends with *. PLSQL data types scalar: numeric (BINARY INTEGER, PLS INTEGER, BINARY FLOAT, BINARY DOUBLE, NUMBER subtypes: DEC, DECIMAL, or NUMERIC, DOUBLE PRECISION or FLOAT, INT, INTEGER, or SMALLINT, REAL) character (CHAR, VARCHAR2, RAW, NCHAR, NVARCHAR2, LONG, LONG RAW, ROWID, UROWID) BOOLEAN 2

3 Date and time (DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, TIMESTAMP WITH LOCAL TIME ZONE) Interval (INTERVAL YEAR TO MONTH, INTERVAL DAY TO SECOND) composite (collections: associative array, nested table, varray; records), reference (REF CURSOR, REF object type), large object (BFILE, BLOB, CLOB, NCLOB), user-defined PLSQL subtypes. 2.1 Variables and Constants Use of Variables Temporary storage of data Manipulation of stored values Reusability Requirements for Variable Names Must start with a letter Can include letters or numbers Can include special characters Must contain no more than 30 characters Must not include reserved words Handling Variables Variables are: Declared and optionally initialized in the declarative section Used and assigned new values in the executable section Passed as parameters to PLSQL subprograms Used to hold the output of a PLSQL subprogram Declaring and Initializing identifier [CONSTANT] datatype [NOT NULL] [{:= DEFAULT} expr]; Examples: v_age NUMBER(3); v_gender VARCHAR2(9); v_i NUMBER(4) NOT NULL := 0; v_sum NUMBER(10) DEFAULT 0; c_pi CONSTANT NUMBER := ; 3

4 Declaring and Initializing v_first_name VARCHAR2(20) := Anna ; v_last_name VARCHAR2(30); v_last_name := Scott ; DBMS_OUTPUT.PUT_LINE( My name is v_first_name v_last_name); Special characters in strings Use additional single quotation mark: v_string VARCHAR2(20) := I m learning ; Specification of delimiter with q notation: v_string := q!i m listening! ; v_string := q [I m bored] ; Specification of delimiter with nq notation (for NCHAR or NVARCHAR types): v_nstr NVARCHAR2(20) := nq <I m sleeping> ; v_nstr := nq {I m dreaming} ; %TYPE %TYPE attribute is used to declare variable according to a database column definition or another declared variable. identifier table.column_name%type; Examples v_first_name employees.first_name%type; v_last_name employees.last_name%type; RECORD Declaration: TYPE record_name IS RECORD ( field1 datatype [NOT NULL] [initialization] [, field2 datatype [NOT NULL] [initialization]...] ); variable_name record_name; Example: TYPE r_address IS RECORD ( v_street VARCHAR2(30), v_num VARCHAR2(4), v_loc VARCHAR2(4) ); vr_address r_address; 4

5 %ROWTYPE record_variable table%rowtype; Example: vr_employee employees%rowtype; Bind Variables Created in the environment Also called host variables Created with the VARIABLE keyword Used in SQL and PLSQL Accessed even after the PLSQL block is executed Referenced with a preceding colon Bind Variables VARIABLE b_salary NUMBER; :b_salary := 2500; PRINT b_salary Data Type Convertion Implicit conversion Characters and numbers Characters and dates Explicit converstion use built-in functions (for example To_char, To_number, To_date, To_timestamp) user defined functions Variable Scope and Visibility The scope of a variable is the part of the program in which the variable is declared and visible The visibility of a variable is the portion of the program where the varaiable can be accessed without using a qualifier outer 5

6 2.2 Operators Operators in PLSQL The same as in SQL: logical (And, OR, NOT) arithmetic (+,-,,*) concatenation ( ) comparison (=,<>,!=,<,<=,>,>=, IS NULL, IS NOT NULL, LIKE, BETWEEN, IN) negation (-) parentheses Additional operator for exponentation (**) 2.3 SQL in PLSQL SQL in PLSQL How to embed SQL within PLSQL? Built-in SQL functions In procedural statements we can use built-in SQL single row functions (Upper, Length, Substr, Round, Last_day, To_char etc.) we can not use DECODE and aggregation functions Sequences v_id NUMBER; v_id := emp_seq.nextval; SQL in PLSQL Inside PLSQL we can use some of SQL statements: queries: SELECT with INTO, DML: INSERT, UPDATE, DELETE, MERGE, TCL: COMMIT, ROLLBACK, SAVEPOINT, SET TRANSACTION, LOCK. SELECT Statement SELECT statement must return only one row!!! The INTO clause is required!!! The names of database columns take precedence over the names of local variables!!! SELECT select_list INTO {variables_list record_name} FROM...; 6

7 SELECT example v_first_name employees.first_name%type; SELECT first_name INTO v_first_name FROM employees WHERE employee_id = 200; DBMS_OUTPUT.PUT_LINE( First name is v_first_name); SQL in PLSQL We don t have to change syntax of INSERT, UPDATE and DELETE statements, but we have additionally RETURNING expr INTO variable: INSERT INTO departments (department_id, department_name) VALUES (90, Entertainment ) RETURNING department_id INTO v_id; We can also use records: INSERT INTO table VALUES record_variable; UPDATE table SET ROW = record_variable WHERE cond; 2.4 Control structures IF IF condition THEN statements; END IF; IF condition THEN statemnts1; ELSE statements2; END IF; IF condition1 THEN statements1; ELSIF condition2 THEN statements2;... ELSE statemnents_n; END IF; 7

8 CASE CASE selector WHEN expression1 THEN instruction1; WHEN expression2 THEN instruction2;... [ELSE instruction_n]; END CASE; CASE WHEN condition1 THEN instruction1; WHEN condition2 THEN instruction2;... [ELSE instruction_n]; END CASE; Loops LOOP instructions; EXIT [WHEN condition]; END LOOP; WHILE condition LOOP instructions; END LOOP; FOR counter IN [REVERSE] min..max LOOP instructions; END LOOP; Sugested Use of Loops Use the basic loop when the ststaments inside the loop must execute at least once Use the WHILE loop if the condition must be evaluated at the start of each iteration 8

9 Use a FOR loop if the number of iterations is known Loop example v_total SIMPLE_INTEGER := 1; FOR i IN LOOP v_total := v_total + i; DBMS_OUTPUT.PUT_LINE( Value is v_total); END LOOP; CONTINUE Statement Adds the functionality to begin the next loop iteration Gives the ability to transfer control to the next iteration of the loop Uses parallel structure and semantics to the EXIT statements Loop with CONTINUE example v_total SIMPLE_INTEGER := 0; v_small SIMPLE_INTEGER := 1; FOR i IN LOOP v_total := v_small + i; DBMS_OUTPUT.PUT_LINE( Total value in iteration i is v_total); CONTINUE WHEN i > 5; v_small := v_small + i; DBMS_OUTPUT.PUT_LINE( Small value in iteration i is v_small); END LOOP; NULL statement IF condition THEN instructions; ELSE NULL; END IF; 9

10 3 Summary Summary PLSQL allows you to use: use variables, constants, control instructions, sequential processing - oriented on data, and many others, as in the next lecture... 4 Resources Resources M. Lentner, Oracle 9i Kompletny podręcznik użytkownika, PJWSTK - W-wa, aspx 10