Postgres Interview Questions And Answers

Most targeted up-to-date Postgres interview questions and answers list

Table of Contents

1. What is a query in PostgreSQL?
2. How do you create a basic select query in PostgreSQL?
3. What is a parameterized query in PostgreSQL?
4. How can you calculate a field's value in a PostgreSQL query?
5. What is a join in PostgreSQL?
6. What is a subquery in PostgreSQL?
7. How do you sort query results in ascending or descending order in PostgreSQL?
8. What is a wildcard character in PostgreSQL queries?
9. How do you use a wildcard in a PostgreSQL query?
10. What is a limit query in PostgreSQL?
11. How do you perform grouping and aggregate functions in PostgreSQL?

• Whats more?
• Contributing
• License

1. What is a query in PostgreSQL?

In PostgreSQL, a query is a request for data retrieval or manipulation from one or more tables in a database. It allows you to filter, sort, calculate, and summarize data based on specific criteria.

2. How do you create a basic select query in PostgreSQL?

To create a select query in PostgreSQL, you can use the SELECT statement.

Here's an example:

SELECT column1, column2 FROM tableName;

3. What is a parameterized query in PostgreSQL?

A parameterized query in PostgreSQL allows you to pass dynamic values as parameters into your query. It helps prevent SQL injection and provides flexibility.

Here's an example:

SELECT column1, column2 FROM tableName WHERE column1 = $1;

4. How can you calculate a field's value in a PostgreSQL query?

You can use calculated fields in PostgreSQL queries to perform calculations on existing data or combine multiple fields. Here's an example that calculates the total price based on unit price and quantity:

SELECT productName, unitPrice, quantity, (unitPrice * quantity) AS totalPrice FROM tableName;

5. What is a join in PostgreSQL?

In PostgreSQL, a join combines records from two or more tables based on a related column between them. It allows you to retrieve data from multiple tables simultaneously. Here's an example of an inner join:

SELECT column1, column2 FROM table1 INNER JOIN table2 ON table1.column = table2.column;

6. What is a subquery in PostgreSQL?

A subquery in PostgreSQL is a query nested inside another query. It is used to retrieve data based on the results of an inner query. Here's an example:

SELECT column1, column2 FROM tableName WHERE column1 IN (SELECT column1 FROM subTable);

7. How do you sort query results in ascending or descending order in PostgreSQL?

To sort query results in PostgreSQL, you can use the ORDER BY clause followed by the column name and the keywords ASC (ascending) or DESC (descending). Here's an example:

SELECT columnName FROM tableName ORDER BY columnName ASC;

8. What is a wildcard character in PostgreSQL queries?

In PostgreSQL, a wildcard character is a special symbol used in query patterns to match one or more characters. The percentage sign (%) represents multiple characters, and the underscore (_) represents a single character.

9. How do you use a wildcard in a PostgreSQL query?

You can use the LIKE operator along with wildcard characters to filter data based on specific patterns in PostgreSQL. Here's an example:

SELECT columnName FROM tableName WHERE columnName LIKE 'A%';

10. What is a limit query in PostgreSQL?

A limit query in PostgreSQL allows you to restrict the number of records returned by a query. It is used to retrieve a specific number of rows. Here's an example:

SELECT columnName FROM tableName LIMIT 10;

11. How do you perform grouping and aggregate functions in PostgreSQL?

In PostgreSQL, you can use the GROUP BY clause along with aggregate functions such as SUM, COUNT, AVG, etc., to perform calculations on grouped data. Here's an example:

SELECT column1, SUM(column2) FROM tableName GROUP BY column1;

What's more?

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Contributing

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License

MIT License