In PostgreSQL, a variable is a meaningful name for a memory location. A variable holds a value that can be changed through the block or function. A variable is always associated with a particular data type. Before using a variable, you must declare it in the declaration section of the PostgreSQL Block. The following illustrates the syntax of declaring a variable.
Syntax: variable_name data_type [:= expression];
Let’s analyze the above syntax:
- First, specify the name of the variable. It is a good practice to assign a meaningful name to a variable. For example, instead of naming a variable “i“ one should use index or counter.
- Second, associate a specific data type with the variable. The data type can be any valid PostgreSQL data type such as INTEGER, NUMERIC, VARCHAR, and CHAR.
- Third, optionally assign a default value to a variable. If you don’t, the initial value of the variable is initialized to NULL.
DO $$ DECLARE counter INTEGER := 1; first_name VARCHAR(50) := 'John'; last_name VARCHAR(50) := 'Doe'; payment NUMERIC(11,2) := 20.5; BEGIN RAISE NOTICE '% % % has been paid % USD', counter, first_name, last_name, payment; END $$;
DO $$ DECLARE created_at time := NOW(); BEGIN RAISE NOTICE '%', created_at; PERFORM pg_sleep(10); RAISE NOTICE '%', created_at; END $$;
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