Constants

In PostgreSQL, constants are fixed values that do not change during execution. They are primarily used in queries and expressions to represent literal values like strings, integers, and boolean values. Constants are mostly used to improve readability and simplify code in functions, WHERE clauses, and SELECT statements.

Syntax

In PL/pgSQL, the below syntax can be used to define a constant within a query:

constant_name CONSTANT data_type := expression;

• constant_name: It is the name of the constant used within the query.
• CONSTANT: It is the keyword used for representing a constant.
• data_type: It specifies the type of data that the constant holds.
• :=: It is an assignment operator used in PL/pgSQL.
• expression: It represents the value that the constant will be initialized with.

Example

Here’s an example of how constants can be defined in PostgreSQL:

DO $$
DECLARE
  -- Declaring a constant with 'FLOAT' as the data type
  pi_value CONSTANT FLOAT := 3.14159;
  -- Declaring a constant with 'TEXT' (string) as the data type
  message CONSTANT TEXT := 'Hello, PostgreSQL!';
BEGIN
  -- Using the constant in a query
  RAISE NOTICE 'Value of pi: %, Message: %', pi_value, message;
END;
$$;

When the above code is executed, PostgreSQL prints the following message:

NOTICE: Value of pi: 3.14159, Message: Hello, PostgreSQL!

Here, the constants pi_value and message are defined.