The main difference between these filters is: The WHERE and HAVING clauses filter data and restrict unwanted data from appearing in your result set. What’s the Difference Between the WHERE and HAVING Clauses in PostgreSQL?Īnother question that interviewers may use to gauge your knowledge of PostgreSQL is to ask you the difference between the WHERE and HAVING clauses. MAX(): Returns the largest value from a set.īeing able to recall what each function does should be sufficient however, if you would like to see practical examples of each aggregate function, check out this article.MIN(): Returns the smallest value from a set.AVG(): Calculates the average column value.SUM(): Calculates the total of all values in a column or an expression.COUNT(): Returns the number of rows that fit the criteria stated in the WHERE clause.There are five aggregate functions in SQL: As mentioned previously, aggregate functions are often used alongside the GROUP BY clause, but there are many possible uses for these functions. In PostgreSQL, aggregate functions perform a calculation over multiple rows and return one value. Check out this post about GROUP BY extensions just in case the topic comes up during an interview. GROUP BY also has GROUP BY extensions, which are a more advanced topic. (Note: Aggregate functions are covered in more detail in the next section.) Here’s what the query would look like: If you want to find the count of each product type, you can use GROUP BY with the COUNT() aggregate function. In your database, you have a table that stores information about the inventory you have in stock. Imagine you have an eCommerce website that sells several product types. Organizing data into groups is useful in making sense of data and in the use of aggregate functions. The GROUP BY clause allows you to group the data that results from your queries. Thus, you may be asked how the GROUP BY clause works in PostgreSQL. Knowing the GROUP BY clause can demonstrate a slightly more advanced knowledge of SQL. For more details, check out this overview of PostgreSQL data types. These were just some of the most notable types that PostgreSQL supports. JSON: The JSON data type stores JSON (JavaScript Object Notation) data.XML: The XML data type stores XML data.An example of an ENUM type might be the days of the week, or a set of status values for a piece of data”. They are equivalent to the ENUM types supported in a number of programming languages. Enumerated Types: “Enumerated (ENUM) types comprise a static, ordered set of values.Boolean: Boolean values store only TRUE, FALSE, and NULL values.Date/Time Types: These store dates, times, or dates and times (timestamps).Binary Data Types: A binary string is a sequence of bytes.The notations VARCHAR(n) and CHAR(n) are aliases for character varying(n) and character(n).” Both of these types can store strings up to n characters in length. Character Types: SQL defines two primary character types: “character varying( n) and character( n), where n is a positive integer. Numeric Types: “Numeric types consist of two, four, and eight-byte integers four and eight-byte floating-point numbers and selectable-precision decimals.”.Check some of the most notable data types below: PostgreSQL supports the common SQL data types it also supports some unexpected ones, such as JSON. What Data Types Are Available in PostgreSQL? It has also fostered a strong community that strives to keep it on the cutting edge of design and functionality.Ĭheck out this article to learn more about the history of PostgreSQL. It is an open-source, relational database that offers security and an impressive feature set. PostgreSQL is quickly becoming one of the most popular databases. Let’s get started! Top 10 Postgres Job Interview Questions 1. We’ve previously covered common questions you can expect at a SQL job interview, but this article will be focused on Postgres specifically. Interviewing and getting asked technical questions about PostgreSQL is even more of a challenge! In this article, we’ll cover some of the PostgreSQL interview questions you can expect when applying for a new job.īy the end of the article, you should be able to handle most of the questions you are likely to face.
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