How to perform complex queries and join tables in PostgreSQL?

Complex queries and table joins in PostgreSQL are typically achieved using SQL statements. Here are some common methods:

1. Use the JOIN operator to connect tables.

SELECT *
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;

1. Utilize subqueries:

SELECT *
FROM table1
WHERE column_name IN (SELECT column_name FROM table2);

1. Merge multiple query results using the UNION operator.

SELECT column1 FROM table1
UNION
SELECT column2 FROM table2;

1. Create temporary table using WITH clause.

WITH temp_table AS (
SELECT *
FROM table1
)
SELECT *
FROM temp_table
INNER JOIN table2 ON temp_table.column_name = table2.column_name;

1. Utilize a correlated subquery:

SELECT *
FROM table1
WHERE EXISTS (
SELECT *
FROM table2
WHERE table1.column_name = table2.column_name
);

These are some common methods that you can choose from based on your specific situation for performing complex queries and joining tables.