PL/sql records

PL/SQL Records

What are records?

Records are another type of datatypes which oracle allows to be defined as a placeholder. Records are composite datatypes, which means it is a combination of different scalar datatypes like char, varchar, number etc.  Each scalar data types in the record holds a value. A record can be visualized as a row of data. It can contain all the contents of a row.
Declaring a record:
To declare a record, you must first define a composite datatype; then declare a record for that type.
The General Syntax to define a composite datatype is:

TYPE record_type_name IS RECORD

(first_col_name column_datatype,

second_col_name column_datatype, ...);

    record_type_name – it is the name of the composite type you want to define.
    first_col_name, second_col_name, etc.,- it is the names the fields/columns within the record.
    column_datatype defines the scalar datatype of the fields.


There are different ways you can declare the datatype of the fields.

1) You can declare the field in the same way as you declare the fieds while creating the table.
2) If a field is based on a column from database table, you can define the field_type as follows:

col_name table_name.column_name%type;

By declaring the field datatype in the above method, the datatype of the column is dynamically applied to the field.  This method is useful when you are altering the column specification of the table, because you do not need to change the code again.
NOTE: You can use also %type to declare variables and constants.

The General Syntax to declare a record of a uer-defined datatype is:

record_name record_type_name;

The following code shows how to declare a record called employee_rec based on a user-defined type.

DECLARE

TYPE employee_type IS RECORD

(employee_id number(5),

 employee_first_name varchar2(25),

 employee_last_name employee.last_name%type,

 employee_dept employee.dept%type);

 employee_salary employee.salary%type;

 employee_rec employee_type;

If all the fields of a record are based on the columns of a table, we can declare the record as follows:

record_name table_name%ROWTYPE;

For example, the above declaration of employee_rec can as follows:

DECLARE

 employee_rec employee%ROWTYPE;

The advantages of declaring the record as a ROWTYPE are:
1)  You do not need to explicitly declare variables for all the columns in a table.
2) If you alter the column specification in the database table, you do not need to update the code.

The disadvantage of declaring the record as a ROWTYPE is:
1) When u create a record as a ROWTYPE, fields will be created for all the columns in the table and memory will be used to create the datatype for all the fields. So use ROWTYPE only when you are using all the columns of the table in the program.

NOTE: When you are creating a record, you are just creating a datatype, similar to creating a variable. You need to assign values to the record to use them.

The following table consolidates the different ways in which you can define and declare a pl/sql record.

Syntax    

Usage

TYPE record_type_name IS RECORD (column_name1 datatype, column_name2 datatype, ...);
   

Define a composite datatype, where each field is scalar.

col_name table_name.column_name%type;
   

Dynamically define the datatype of a column based on a database column.

record_name record_type_name;
   

Declare a record based on a user-defined type.

record_name table_name%ROWTYPE;
    Dynamically declare a record based on an entire row of a table. Each column in the table corresponds to a field in the record.

Passing Values To and From a Record

When you assign values to a record, you actually assign values to the fields within it.
The General Syntax to assign a value to a column within a record direclty is:

record_name.col_name := value;

If you used %ROWTYPE to declare a record, you can assign values as shown:

record_name.column_name := value; 

We can assign values to records using SELECT Statements as shown:

SELECT col1, col2

INTO record_name.col_name1, record_name.col_name2

FROM table_name

[WHERE clause];
If %ROWTYPE is used to declare a record then you can directly assign values to the whole record instead of each columns separately. In this case, you must SELECT all the columns from the table into the record as shown:

SELECT * INTO record_name

FROM table_name

[WHERE clause];

Lets see how we can get values from a record.
The General Syntax to retrieve a value from a specific field into another variable is:

var_name := record_name.col_name;

The following table consolidates the different ways you can assign values to and from a record:
Syntax    

Usage

record_name.col_name := value;
   

To directly assign a value to a specific column of a record.

record_name.column_name := value;
   

To directly assign a value to a specific column of a record, if the record is declared using %ROWTYPE.

SELECT col1, col2 INTO record_name.col_name1, record_name.col_name2 FROM table_name [WHERE clause];
   

To assign values to each field of a record from the database table.

SELECT * INTO record_name FROM table_name [WHERE clause];
   

To assign a value to all fields in the record from a database table.

variable_name := record_name.col_name;
   

To get a value from a record column and assigning it to a variable.

PL/sql condition statements

Conditional Statements in PL/SQL

As the name implies, PL/SQL supports programming language features like conditional statements, iterative statements.

The programming constructs are similar to how you use in programming languages like Java and C++. In this section I will provide you syntax of how to use conditional statements in PL/SQL programming.

IF THEN ELSE STATEMENT

1)

IF condition 

THEN 

 statement 1; 

ELSE 

 statement 2; 

END IF;

2)

IF condition 1 

THEN 

 statement 1; 

 statement 2; 

ELSIF condtion2 THEN 

 statement 3; 

ELSE 

 statement 4; 

END IF

3)

IF condition 1 

THEN 

 statement 1; 

 statement 2; 

ELSIF condtion2 THEN 

 statement 3; 

ELSE 

 statement 4; 

END IF;

4)

IF condition1 THEN 

ELSE 

 IF condition2 THEN 

 statement1; 

 END IF; 

ELSIF condition3 THEN 

  statement2; 

END IF;

PL/sql placeholder

Advantages of PL/SQL
These are the advantages of PL/SQL.

    Block Structures: PL SQL consists of blocks of code, which can be nested within each other. Each block forms a unit of a task or a logical module. PL/SQL Blocks can be stored in the database and reused.

     Procedural Language Capability: PL SQL consists of procedural language constructs such as conditional statements (if else statements) and loops like (FOR loops).

     Better Performance: PL SQL engine processes multiple SQL statements simultaneously as a single block, thereby reducing network traffic.
    Error Handling: PL/SQL handles errors or exceptions effectively during the execution of a PL/SQL program. Once an exception is caught, specific actions can be taken depending upon the type of the exception or it can be displayed to the user with a message.

PL/SQL Placeholders

Placeholders are temporary storage area. Placeholders can be any of Variables, Constants and Records. Oracle defines placeholders to store data temporarily, which are used to manipulate data during the execution of a PL SQL block.
Depending on the kind of data you want to store, you can define placeholders with a name and a datatype. Few of the datatypes used to define placeholders are as given below.
Number (n,m) , Char (n) , Varchar2 (n) , Date , Long , Long raw, Raw, Blob, Clob, Nclob, Bfile

PL/SQL Variables

These are placeholders that store the values that can change through the PL/SQL Block.

The General Syntax to declare a variable is:

variable_name datatype [NOT NULL := value ];
    variable_name is the name of the variable.
    datatype is a valid PL/SQL datatype.
    NOT NULL is an optional specification on the variable.
    value or DEFAULT valueis also an optional specification, where you can initialize a variable.
    Each variable declaration is a separate statement and must be terminated by a semicolon.


For example, if you want to store the current salary of an employee, you can use a variable.

DECLARE

salary  number (6);

* “salary” is a variable of datatype number and of length 6.

When a variable is specified as NOT NULL, you must initialize the variable when it is declared.

For example: The below example declares two variables, one of which is a not null.

DECLARE

salary number(4);

dept varchar2(10) NOT NULL := “HR Dept”;
The value of a variable can change in the execution or exception section of the PL/SQL Block. We can assign values to variables in the two ways given below.

1) We can directly assign values to variables.
    The General Syntax is:        

  variable_name:=  value;

2) We can assign values to variables directly from the database columns by using a SELECT.. INTO statement. The General Syntax is:

SELECT column_name

INTO variable_name

FROM table_name

[WHERE condition];

Example: The below program will get the salary of an employee with id '1116' and display it on the screen.

DECLARE

 var_salary number(6);

 var_emp_id number(6) = 1116;

BEGIN

 SELECT salary

 INTO var_salary

 FROM employee

 WHERE emp_id = var_emp_id;

 dbms_output.put_line(var_salary);

 dbms_output.put_line('The employee '

      || var_emp_id || ' has  salary  ' || var_salary);

END;

/

NOTE: The backward slash '/' in the above program indicates to execute the above PL/SQL Block.

Scope of Variables

PL/SQL allows the nesting of Blocks within Blocks i.e, the Execution section of an outer block can contain inner blocks. Therefore, a variable which is accessible to an outer Block is also accessible to all nested inner Blocks. The variables declared in the inner blocks are not accessible to outer blocks. Based on their declaration we can classify variables into two types.

    Local variables - These are declared in a inner block and cannot be referenced by outside Blocks.
    Global variables - These are declared in a outer block and can be referenced by its itself and by its inner blocks.

For Example: In the below example we are creating two variables in the outer block and assigning thier product to the third variable created in the inner block. The variable 'var_mult' is declared in the inner block, so cannot be accessed in the outer block i.e. it cannot be accessed after line 11. The variables 'var_num1' and 'var_num2' can be accessed anywhere in the block.

1> DECLARE

2>  var_num1 number;

3>  var_num2 number;

4> BEGIN

5>  var_num1 := 100;

6>  var_num2 := 200;

7>  DECLARE

8>   var_mult number;

9>   BEGIN

10>    var_mult := var_num1 * var_num2;

11>   END;

12> END;

13> /

PL/SQL Introduction

What is PL/SQL?

PL/SQL stands for Procedural Language extension of SQL.

PL/SQL is a combination of SQL along with the procedural features of programming languages. It was developed by Oracle Corporation in the early 90’s to enhance the capabilities of SQL.


The PL/SQL Engine:

Oracle uses a PL/SQL engine to processes the PL/SQL statements. A PL/SQL code can be stored in the client system (client-side) or in the database (server-side).
About This PL SQL Programming tutorial

This Oracle PL SQL tutorial teaches you the basics of programming in PL/SQL with appropriate examples. You can use this tutorial as your guide or reference while programming with PL SQL. I will be making this Oracle PL SQL programming tutorial as often as possible to share my knowledge in PL SQL and help you in learning PL SQL better.

Even though the programming concepts discussed in this tutorial is specific to Oracle PL SQL. The concepts like cursors, functions and stored procedures can be used in other database systems like Sybase , Microsoft SQL server etc, with some change in syntax. This tutorial will be growing regularly; let us know if any topic related to PL SQL needs to be added or you can also share your knowledge on PL SQL with us. Lets share our knowledge about PL SQL with others.
A Simple PL/SQL Block:

Each PL/SQL program consists of SQL and PL/SQL statements which from a PL/SQL block.

A PL/SQL Block consists of three sections:

    The Declaration section (optional).
    The Execution section (mandatory).
    The Exception (or Error) Handling section (optional).

Declaration Section:
The Declaration section of a PL/SQL Block starts with the reserved keyword DECLARE. This section is optional and is used to declare any placeholders like variables, constants, records and cursors, which are used to manipulate data in the execution section. Placeholders may be any of Variables, Constants and Records, which stores data temporarily. Cursors are also declared in this section.

Execution Section:
The Execution section of a PL/SQL Block starts with the reserved keyword BEGIN and ends with END. This is a mandatory section and is the section where the program logic is written to perform any task. The programmatic constructs like loops, conditional statement and SQL statements form the part of execution section.

Exception Section:
The Exception section of a PL/SQL Block starts with the reserved keyword EXCEPTION. This section is optional. Any errors in the program can be handled in this section, so that the PL/SQL Blocks terminates gracefully. If the PL/SQL Block contains exceptions that cannot be handled, the Block terminates abruptly with errors.

Every statement in the above three sections must end with a semicolon ; . PL/SQL blocks can be nested within other PL/SQL blocks. Comments can be used to document code.

This is how a sample PL/SQL Block looks.

DECLARE
     Variable declaration
BEGIN
     Program Execution
EXCEPTION
     Exception handling
END;