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Oracle Assignments model and language

Assignments model in PL/SQL

All programming languages allow us to assign values to variables. Usually, a value is assigned to variable, standing
on left side. The prototype of the overall assignment operations in any contemporary programming language looks like this:

left_operand assignment_operand right_operand instructions_of_stop

This will assign right operand to the left operand. In PL/SQL this operation looks like this:

left_operand := right_operand;

Left operand must be always a variable. Right operand can be value, variable or function:

SET serveroutput ON
 v_hello1 VARCHAR2(32767);
 v_hello2 VARCHAR2(32767);
 v_hello3 VARCHAR2(32767);
 FUNCTION hello RETURN VARCHAR2 IS BEGIN RETURN 'Hello from a function!'; END;
 -- from a value (string literal)
 v_hello1 := 'Hello from a value!';
 -- from variable
 v_hello2 := v_hello1;
 -- from function
 v_hello3 := hello;

When the code block is executed in SQL*Plus the following output is printed in console:

Hello from a value!
Hello from a value!
Hello from a function!

There is a feature in PL/SQL that allow us to assign "from right to the left". It's possible to do in SELECT INTO statement. Prototype of this instrunction you will find below:

SELECT [ literal | column_value ]
INTO local_variable
FROM [ table_name | aliastable_name ]
WHERE comparison_instructions;

This code will assign character literal to a local variable:

SET serveroutput ON
 v_hello VARCHAR2(32767);
 SELECT 'Hello world!'
 INTO v_hello
 FROM dual;

When the code block is executed in SQL*Plus the following output is printed in console:

Hello world!

Asignment "from right to the left" is not a standard, but it's valuable feature for programmers and users. Generally it's used when programmer is using cursors in PL/SQL - this technique is used, when we want to return a single scalar value or set of columns in the one line of cursor from SQL cursor.


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