How to use declare in Oracle

The DECLARE statement is the keyword used in Oracle to declare variables, constants and cursors. Provides a convenient way to define and initialize data objects for use in PL/SQL blocks. By using the DECLARE statement, PL/SQL code can be made more modular and readable.

The DECLARE statement in Oracle is a keyword used to declare variables, constants and cursors in PL/SQL blocks. The DECLARE statement is typically used to define variables and constants for use in PL/SQL blocks.

The basic syntax of the DECLARE statement is as follows:

variable_name [CONSTANT] [datatype] [:= initial_value];
BEGIN
-- PL/SQL code

In the DECLARE statement, multiple variables and constants can be declared, and each declaration is separated by a semicolon. The following are some common uses of the DECLARE statement:

1. Declare variables:

In the DECLARE statement, you can use the VAR keyword to declare a variable and specify its data type and initial value. For example:

emp_name VARCHAR2(50) := 'John Smith';
emp_salary NUMBER := 5000;
BEGIN
-- PL/SQL code

2. Declare a constant:

In the DECLARE statement, you can use the CONSTANT keyword to declare a constant and specify its data type and value. The value of a constant cannot be modified after it is declared. For example:

pi CONSTANT NUMBER := 3.14159;
max_attempts CONSTANT INTEGER := 3;
BEGIN
-- PL/SQL code

3. Declare a cursor:

In the DECLARE statement, you can use the CURSOR keyword to declare a cursor and specify its query statement. Cursors are used to traverse and manipulate query result sets within PL/SQL blocks. For example:

CURSOR emp_cursor IS
SELECT emp_id, emp_name, emp_salary FROM employees;
BEGIN
-- PL/SQL code

4. Declare record type:

In the DECLARE statement, you can use the TYPE keyword to declare a record type and define its fields. Record types can be used to store and manipulate values ​​from multiple related fields. For example:

TYPE emp_record IS RECORD (
emp_id NUMBER,
emp_name VARCHAR2(50),
emp_salary NUMBER
);
emp emp_record;
BEGIN
-- PL/SQL code

In the DECLARE statement, you can also use other keywords and syntax to define more complex variables and constants, such as table types, index types, object types, etc. The DECLARE statement is typically used to declare and initialize variables and constants in PL/SQL blocks for use in subsequent PL/SQL code. Variables and constants declared in the DECLARE statement are only visible in the current PL/SQL block and will be destroyed after the block ends.

To summarize, the DECLARE statement is the keyword used in Oracle to declare variables, constants and cursors. It provides a convenient way to define and initialize data objects used in PL/SQL blocks. By using the DECLARE statement, you can make your PL/SQL code more modular and readable .

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