Understanding Nested Select Statement in PL/SQL

The nested select statement in PL/SQL is a feature that allows for the retrieval of data from multiple tables in a single query. It involves using a SELECT statement within another SELECT statement to fetch data based on specified conditions.

The main concept of a nested select statement in PL/SQL involves using a SELECT statement within another SELECT statement. This allows for the retrieval of data from multiple tables or views based on specified conditions. The syntax for a nested select statement is as follows:

Syntax:

-- Outer SELECT Statement: Retrieves data from table1 based on conditions

SELECT column1, column2, ...
FROM table1
WHERE condition IN (

    -- Nested SELECT Statement: Retrieves data from table2 based on separate conditions

    SELECT column3, column4, ...
    FROM table2
    WHERE condition
);

Explanation of Syntax:

Outer SELECT Statement:

• The outer SELECT statement start the query execution by specifying the columns (column1, column2, etc.) which we want to retrieve from table1 and generally defines the foundation of the query and indicates the primary data source.

Nested SELECT Statement:

• Nested within the IN clause of the outer SELECT statement.This inner query selects specific columns (column3, column4, etc.) from table2 and operates independently and retrieving data from table2 based on its own set of conditions.

PL/SQL is a Procedural Language/Structured Query Language and it enables users to write procedural logic directly within the database, including procedures, functions, triggers, and packages. In this article, we will understand Nested select statements in PL/SQL along with the examples and so on.