Ms Sql Server

Jorge Sandoval

15 SQL Server Practice Exercises with Solutions

Enhance your SQL Server proficiency with our SQL Server practice exercises. Each of these 15 practical T-SQL tasks includes a detailed solution to help you improve your querying skills. You know how everyone says, "Practice makes perfect"? Well, it couldn't be truer for SQL. The real learning happens when you start working with queries, tables, and data. If you're looking to sharpen your skills in MS SQL Server, you're in the right spot.

Jill Thornhill

Integrating SQL with Python for Data Analysis

Integrating SQL with Python isn’t difficult. The two tools work together to combine the information-processing power of relational databases with the flexibility of a programming language. In this article, I will discuss the benefits of data analysis using SQL and Python, with real-world coding examples. Why do most of the best data analysis tools on the market – such as Tableau and Power BI – include both SQL and Python in their toolboxes?

Tihomir Babic

SQL Server Date Functions: A Data Analysis Guide

Date functions are the bread and butter of data analysis and reporting with SQL Server. In this guide, I will show you practical examples of the use of SQL Server date functions and how to apply them to your reports. A question for all data analysts: Do you want to be taken seriously? I’m sure you do. In that case, knowing SQL Server date functions is mandatory. Date and time data types are ubiquitous in databases, as they are essential for reporting.

Tihomir Babic

Top 29 SQL Server Interview Questions

Looking for an SQL Server job? Review these 29 must-know SQL Server interview questions and you’ll be well-prepared. And don’t worry about looking up the answers – we provide them, too! Microsoft SQL Server's first version was released in 1989 and has a rich history. It has come a long way since then, becoming one of the most used database engines in the data industry. In the last ten years, it’s been the third most popular database engine.

LearnSQL.com Team

SQL Server Cheat Sheet

Welcome to the SQL Server Cheat Sheet! Whether you're just starting out with SQL Server or you're a seasoned developer looking for a quick reference, this guide is tailored for you. This cheat sheet is a comprehensive guide to SQL Server, offering a quick reference to its essential commands. It covers the basics of creating and displaying databases and tables, the commands to modify tables, and the fundamental syntax for T-SQL commands such as SELECT, INSERT, UPDATE, and DELETE.

Ignacio L. Bisso

CTE in T-SQL: A Beginner’s Guide with 7 Examples

A common table expression (CTE) is a powerful T-SQL feature that simplifies query creation in SQL Server. CTEs work as virtual tables (with records and columns) that are created on the fly during the execution of a query. They are consumed by the query and destroyed after the query executes. In some cases – like when the query expects data in a specific format and the source tables have the data in another format – a CTE can act as a bridge to transform the data in the source tables to the format expected by the query.

Jill Thornhill

How to Learn T-SQL Querying

T-SQL is the dialect of SQL used by Microsoft SQL Server databases. Find out the best way to learn T-SQL querying with interactive online courses. In today's data-driven world, increasing your database knowledge is always a good choice. Microsoft SQL Server is one of the most popular databases nowadays. Knowing T-SQL – the query language of SQL Server databases –is often recommended as a worthwhile skill for careers in IT, business, or research fields.

Nicole Darnley

How to Write a Recursive CTE in SQL Server

A guide to understanding and using recursive CTEs in SQL Server SQL Server offers a lot of powerful tools for working with data, including Common Table Expressions (CTEs). A CTE is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. CTEs can break down long queries into smaller, more manageable pieces of logic and make them more readable. SQL Server offers recursive Common Table Expressions.

Martyna Sławińska

How to Export Data From Microsoft SQL Server to a CSV File

When working with data and databases, it is common to export data for further processing or transport to another database. Follow this article to learn how to export data from Microsoft SQL Server to a CSV file. In this article, we first recall what a CSV file is and why you would want to export data in this format from an MS SQL Server database. Then, we cut to the chase and export data to a CSV file using both SQL Server Management Studio (SSMS) and SQL Command Line (SQLCMD).

Jakub Romanowski

SQL Track of the Season: SQL from A to Z in MS SQL Server

Maybe your company uses MS SQL Server and you’d like to join the data analysis team. Or maybe you want to add a new skill to your CV. Either way, our SQL Track of the Season: SQL from A to Z in MS SQL Server, will help. In this article, I’ll answer common questions about this awesome set of online MS SQL Server courses. If you’re reading this blog post, you probably already know that you should start learning SQL and working with databases.

Tihomir Babic

An Overview of Microsoft SQL Server Text Functions

Data analysts use text values when creating SQL reports. You can create your own labels with functions, classify rows based on text value, or do computations based on it. This article covers how to do all that. The text values in databases are not just for reading. As with numeric values, we perform operations on them and manipulate the text. SQL Server has a fair number of text functions.

Jakub Romanowski

Top 5 MS SQL Server Courses for Beginners

Every journey, including a career change, begins with the first step. If you're thinking about learning data analysis or strengthening your MS SQL Server skills arsenal, you've come to the right place. Here are the top 5 MS SQL Server online courses. Enjoy! You've probably heard that today’s organizations rely heavily on data analysis. You heard right. They are looking for employees who can navigate the world of databases and draw conclusions from data.

Kateryna Koidan

SQL Date and Time Functions in 5 Popular SQL Dialects

Are you confused by all the date and time functions used across different SQL dialects? In this article, I summarize the date and time data types used in PostgreSQL, Oracle, SQLite, MySQL, and T-SQL. I also provide examples with the key SQL date and time functions used across these dialects. It’s time to become date and time gurus! Do you want to calculate how often employees are running late for work?

Martyna Sławińska

An Overview of MS SQL Server Data Types

SQL Server data types define what can be stored in a column, local variable, expression, or parameter. It is essential to pick the right data type. Ultimately. your choice of data types affects the whole database. Read on to learn about all of the data types available in MS SQL Server. In this article, we’ll cover numerical, text, and date and time data type categories in detail. We’ll go through their syntax, storage size, and typical use cases.

Jakub Romanowski

Free Course of the Month: SQL Reports in SQL Server

This is another in our series of free SQL Courses of the Month. This time, you can learn SQL Reporting in MS SQL Server for free. Do you want to be able to prepare even better SQL reports? Or maybe you have some basic knowledge of SQL Server (one of the major SQL dialects) and would like to go a step further? This is the course for you.

Dorota Wdzięczna

How to Install MS SQL Server 2019 on Windows

Do you want to install SQL Server 2019 on your Windows PC? How about the latest version of SQL Server Management Studio? I’ll walk you through the process. Soon you’ll be writing T-SQL queries and operating on SQL Server databases! As I write this article, Microsoft SQL Server 2019 is the latest version of SQL Server. It’s the 15th version of one of the most popular database servers in the world.

Jakub Romanowski

Is MS SQL Server Still Worth Learning in 2024?

Updated on: March 10, 2024 MS SQL Server is an in-demand skill in today’s job market. Should you learn  MS SQL Server in 2024? In this article, I’ll answer this question. Thinking about whether you should dive into Microsoft SQL Server in 2024 – especially with so many free database alternatives available? MS SQL Server has been a go-to for handling data for ages, thanks to its solid features and reliability.

Jakub Romanowski

Where Can I Find Good Courses to Practice MS SQL Server?

Updated on: April 6, 2024 Begin your journey to mastering MS SQL Server with the finest practice exercises out there. Whether you are a beginner or seeking to improve your T-SQL skills, explore the top destinations for the most engaging and interactive MS SQL practice courses online. You've started learning MS SQL Server. Maybe you've done a course, watched some YouTube tutorials, and feel pretty confident in your knowledge. What now?

How to Find the Difference Between Two Datetimes in T-SQL

Problem: You have two columns of the type datetime and you want to calculate the difference between them. Example: In the travel table, there are three columns: id, departure, and arrival. You'd like to calculate the difference between the arrival and the departure. The travel table looks like this: iddeparturearrival 12018-03-25 12:00:002018-04-05 07:30:00 22019-09-12 15:50:002019-10-23 10:30:30 32018-07-14 16:15:002018-07-14 20:40:30 42018-01-05 08:35:002019-01-08 14:00:00 Solution 1 (difference in seconds): SELECT id, departure, arrival, DATEDIFF(second, departure, arrival) AS difference FROM travel; The result is:

How to Group by Two Columns in SQL

Problem: You want to group your data by two columns so you can count some statistics. Example: In the order table, you have the columns order_date, product_id, customer_id, and number. You would like to count the number of products bought by each customer each day. The order table looks like this: order_dateproduct_idcustomer_idnumber 2023-11-25711 2023-11-251213 2023-11-265312 2023-11-26124 2023-11-26321 2023-11-261627 2023-11-26332 2023-11-27631 Solution: SELECT order_date, customer_id, SUM(number) AS products_number FROM order GROUP BY order_date, customer_id; The result is:

How to Delete a Foreign Key Constraint in SQL

Problem: You want to delete a foreign key from a table in a database. Example: We want to remove the foreign key named fk_student_city_id from the table student. Solution: ALTER TABLE student DROP CONSTRAINT fk_student_city_id; Discussion: To delete a foreign key from a table, use the ALTER TABLE clause with the name of the table (in our example, student) followed by the clause DROP CONSTRAINT with the name of the foreign key constraint.

How to Create a Table with a Foreign Key in SQL

Problem: You want to create a foreign key for a table in a database. Example: We would like to create a table named student that contains a foreign key that refers to the id column in the table city. Solution 1: Creating new table with single-column foreign key CREATE TABLE student ( id INT PRIMARY KEY, first_name VARCHAR(100) NOT NULL, last_name VARCHAR(100) NOT NULL, city_id INT FOREIGN KEY REFERENCES city(id) ); Discussion: To create a new table containing a foreign key column that references another table, use the keyword FOREIGN KEY REFERENCES at the end of the definition of that column.

How to Calculate the Difference Between Two Dates in T-SQL

Problem: You have two columns of the date type and you want to calculate the difference between them. Example: In the travel table, there are three columns: id, departure, and arrival. You'd like to calculate the difference between arrival and departure, or the number of days from arrival to departure inclusively. The travel table looks like this: iddeparturearrival 12018-03-252018-04-05 22019-09-122019-09-23 32018-07-142018-07-14 42018-01-052018-01-08 Solution: SELECT id, departure, arrival, DATEDIFF(day, departure, arrival) AS date_difference, DATEDIFF(day, departure, arrival) + 1 AS days_inclusive FROM travel; The result is:

How to remove a unique constraint in SQL?

Problem: You would like to remove a unique constraint from the column/columns in a table in a database. Example: We would like to drop the unique constraint in the table product from the column name. The statement below shows how to do it. Solution ALTER TABLE product DROP CONSTRAINT UQ_product_name In this example the table product is altered by using the ALTER TABLE clause. After this clause you enter the name of the table (in our example: product) and the clause DROP CONSTRAINT with the name of the unique constraint you want to remove.

How to Make a Column Unique in SQL?

Problem: You would like to make a column unique in a given table in a database. Example: We would like to make the column name unique in the table product. The query below presents one way to do it. Solution 1: Creating new table with a UNIQUE constraint CREATE TABLE product ( id INT NOT NULL PRIMARY KEY, name VARCHAR(100) UNIQUE, producer VARCHAR(100), category VARCHAR(100) ); Discussion: In this example a given column (the column name) was made unique by adding the clause UNIQUE at the end of the column definition (name VARCHAR(100) UNIQUE).

How to Group by Year in T-SQL

Problem: You want to group your data by year in SQL Server database. Example: One of the columns in your data is transaction_date. It contains a date. You would like to group all your data by year and calculate the total money earned each year. The data table looks like this: transaction_datemoney 2022-03-251700 2023-09-12100 2022-07-141200 2022-01-05400 2023-06-082000 2021-03-061500 Solution 1: Displaying the year and the money earned SELECT YEAR(transaction_date) AS year, SUM(money) AS money_earned FROM data GROUP BY YEAR(transaction_date); The result is:

How to Calculate a Square Root in SQL

Problem: You want to find the square root of a number in SQ:. Example: You want to compute the square root of all numbers in the column number from the table data. number 9 2 1 0.25 0 -4 Solution: SELECT number, SQRT(number) AS square_root FROM data; The result is:

How to Get Yesterday’s Date in T-SQL

Problem: You would like to display yesterday's date (without time) in an SQL Server database. Solution: SELECT DATEADD(day, -1, CAST(GETDATE() AS date)) AS YesterdayDate; Assuming today is 2020-09-24, the result is: yesterday_date 2020-09-23 Discussion: To get yesterday's date, you need to subtract one day from today's date. Use GETDATE() to get today's date (the type is datetime) and cast it to date.

Agnieszka Kozubek-Krycuń

How to Group Data by Week in SQL Server

This is additional content for the LearnSQL.com course Customer Behavior Analysis in SQL Server. In this course, we showed you how you can analyze the customer lifecycle (customer acquisition, conversion, activity, retention, and churn) with SQL. We discussed customer registration cohorts, or groups of customers who registered during the same period (e.g. same week, same month). Analyzing customer registration cohorts lets you see registration trends and relate registration cohorts with marketing campaigns.

How to Subtract 30 Days from a Date in T-SQL

Problem: You’d like to get the date 30 days before a given date in T-SQL. Example: Our database has a table named Computer with data in the columns Id, Name, and PurchaseDate. IdNamePurchaseDate 1Sony GX10002019-01-20 2Samsung LX20002019-04-15 3Dell K802019-08-30 Let’s get the name of each computer and the date 30 days before its purchase date.

How to Get the Year from a Date in T-SQL

Problem: You’d like to get the year from a date field in a SQL Server database. Example: Our database has a table named Children with data in the columns Id, FirstName, LastName, and BirthDate. IdFirstNameLastNameBirthDate 1JaneSmith2018-06-20 2GaryBrown2010-02-02 3LoraAdams2014-11-05 Let’s get the year from each child’s birthdate. Solution: We’ll use the YEAR() function. Here’s the query you would write:

How to Get the Month from a Date in T-SQL

Problem: You’d like to get the month from a date field in a SQL Server database. Example: Our database has a table named Furniture with data in the columns Id, Name, and ProducedDate. IdNameProducedDate 1sofa2018-01-10 2chair2018-01-05 3desk2018-06-20 4bookcase2018-11-15 Let’s get the month from each product’s ProducedDate and find out which furniture was produced in a given month.

How to Get the Last Day of the Month in T-SQL

Problem: You’d like to find the last day of the month for a specific date in T-SQL. Example: Our database has a table named Furniture with data in the columns Id, Name, and PurchaseDate. IdNamePurchaseDate 1sofa2019-02-10 2desk2019-04-01 3bookcase2019-05-20 Let’s get products’ names and purchase dates and the last day of the month when these items were purchased.

How to Get the Day from a Date in T-SQL

Problem: You’d like to get the number of day from a date field in a SQL Server database. For example, from the date of February 27, 2023, you'd like to get the number 27. Example: Our database has a table named MedicalVisit with data in the columns Id, FirstName, LastName, and VisitDate. IdFirstNameLastNameVisitDate 1JaneMiller2019-11-17 2AlexSmith2019-11-20 3WilliamBrown2019-11-20 4AliceThomas2019-11-05 For each patient, let’s find the day of the medical visit.

How to Get the Current Date (Without Time) in T-SQL

Problem: When working with SQL Server, you often need to get the current date without the time component. To achieve this in T-SQL, you can use several straightforward methods. Here, we will show you the most efficient and easiest way. Solution: We’ll use the GETDATE() function to get the current date and time. Then we’ll use the CAST() function to convert the returned datetime data type into a date data type.

How to Get Current Date & Time in T-SQL (No Time Zone)

Problem: You’d like to get the current date and time in T-SQL, but you don’t want the time zone offset. Solution: We’ll use GETDATE(), CURRENT_TIMESTAMP, and SYSDATETIME() to get the current date and time without the time zone offset. The first two functions allow us to get the current time with a lower precision. (GETDATE() is a T-SQL function, while CURRENT_TIMESTAMP is a SQL standard function; both functions return the same data type).

How to Change Date and Time Formats in T-SQL

Problem: You’d like to change the format of a date field or value in a SQL Server database. Example: Our database has a table named Patient with data in the columns Id, FirstName, LastName, and RegistrationDate. IdFirstNameLastNameRegistrationDate 1JaneWilliams2019-06-20 2GabrielBrown2019-02-02 3LoraFolk2016-11-05 Let’s change the format of each patient’s registration date. We’ll put the name of the weekday first, followed by the month day and name and a 4-digit year (e.

How to Add Days to a Date in T-SQL

Problem: You’d like to add a given number of days to a date in T-SQL. Example: Our database has a table named Flight with data in the columns Code and DepartureDate. CodeDepartureDate LT20302023-02-20 GH11002023-03-01 SR54672023-12-30 Let’s change the departure date for all flights, adding two days to the current departure date. Solution: We will use the DATEADD() function to specify the unit of time to add, define how much to add, and select the date to change.

How to Find Rows with Minimum Value

Problem: You want to find rows which store the smallest numeric value in a column. Example: Our database has a table named weather with data in the following columns: id, city, and temperature. You want to find cities with the lowest temperature. idcitytemperature 1Houston23 2Atlanta20 3Boston15 4Cleveland15 5Dallas34 6Austin28 Solution: SELECT id, city, temperature FROM weather WHERE temperature = (SELECT MIN(temperature) FROM weather); Here’s the result:

How to Find Rows with Maximum Value

Problem: You want to find rows which store the largest numeric value in a given column. Example: Our database has a table named student with data in the following columns: id, first_name, last_name, and grade. You want to find the students who have the highest grades. idfirst_namelast_namegrade 1LisaJackson3 2GaryLarry5 3TomMichelin2 4MartinBarker2 5EllieBlack5 6MarySimpson4 Solution: SELECT id, first_name, last_name, grade FROM student WHERE grade = (SELECT MAX(grade) FROM student); Here’s the result:

How to Find Records with NULL in a Column

Problem: You want to find records with NULL in a column. Example: Our database has a table named children with data in four columns: id, first_name, middle_name, and last_name. idfirst_namemiddle_namelast_name 1JohnCarlJackson 2TomNULLThomson 3LisaAliceNULL 4AnneNULLSmith Let’s find the id, first name, and last name of children without a middle name (NULL in column middle_name). We use the IS NULL operator for this. Solution: SELECT id, first_name, last_name FROM children WHERE middle_name IS NULL; Here’s the result:

How to Filter Rows without NULL in a column

Problem: You want to find records without a NULL in a column. Example: Our database has a table named product with data in three columns: id, name, and price. idnameprice 1butterNULL 2milk2.35 3bread3.25 4cheeseNULL Let’s find the names and prices of products that have a price (without a NULL). Do this by using the IS NOT NULL operator.

How to Filter Records with Aggregate Function SUM

Problem: You need to filter groups of rows by the sum of a given column. Example: Our database has a table named company with data in the following columns: id, department, first_name, last_name, and salary. iddepartmentfirst_namelast_namesalary 1marketingLoraBrown2300 2financeJohnJackson3200 3marketingMichaelThomson1270 4productionTonyMiller6500 5productionSallyGreen2500 6financeOlivierBlack3450 7productionJenifferMichelin2800 8marketingJeremyLorson3600 9marketingLouisSmith4200 Let’s find the names of departments that have sums of salaries of its employees less than 7000.

How to Filter Records with Aggregate Function COUNT

Problem: You want to find groups of rows with a specific number of entries in a group. Example: Our database has a table named product with data in the following columns: id, name and category. idnamecategory 1sofafurniture 2glovesclothing 3T-Shirtclothing 4chairfurniture 5deskfurniture 6watchelectronics 7armchairfurniture 8skirtclothing 9radio receiverelectronics Let’s find the category of products with more than two entries.

How to Filter Records with Aggregate Function AVG

Problem: You want to filter groups of rows in by the average value of a given column. Example: Our database has a table named product with data in the following columns: id, name, store and price. idnamestoreprice 1milkGreen Shop2.34 2breadClark’s Grocery3.56 3breadSuper Market4.15 4milkSuper Market1.80 5breadGrocery Amanda2.26 6milkViolet Grocery3.45 7milkClark’s Grocery2.10 8breadViolet Grocery2.

What’s the Difference Between RANK and DENSE_RANK in SQL?

Problem: You want to compare the rankings produced by RANK and DENSE_RANK and add them as new columns to a table. Example: Our database has a table named sales_assistant with data in the following columns: id (primary key), first_name, last_name, month, and sold products. idfirst_namelast_namemonthsold products 1LisaBlack 52300 2MaryJacobs52400 3LisaBlack 62700 4MaryJacobs62700 5AlexSmith 62900 6MaryJacobs71200 7LisaBlack 71200 8AlexSmith 71000 Let’s display each sales assistant’s first and last name and number of sold products.

How to Remove Leading and Trailing Spaces in T-SQL

Problem: You’d like to remove a spaces or a specific characters from the beginning and end of a string in T-SQL. Example: Our database has a table named company with data in two columns: id and name. idname 1' Super Market ' 2'Green shop ' 3' Modern Bookshop' Let’s trim the name of each company to remove the unnecessary space at the beginning and end.

How to Number Rows in SQL

Problem: You would like to give each row in the result table a separate number. Example: Our database has a table named furniture with data in the following columns: code (primary key) and name. codename 101bed 202sofa 333chair 123bookcase 235table 766desk The furniture table stores the name of pieces of furniture that we want to number.

How to Find the Minimum Value of a Column in SQL

Problem: You’d like to find the smallest numeric value in a column. Example: Our database has a table named employment with data in the following columns: id, first_name, last_name, department, and salary. idfirst_namelast_namedepartmentsalary 1EllieMartinesmarketing1200 2MartinJohnsonfinance2300 3MichaelJacobsproduction1100 4StephenKowalskimarketing4300 5StanleyMillermarketing3500 6JenyBrownfinance5000 7MargaretGreenmarketing1500 8LisaThomasproduction2800 Let’s find the lowest salary among all employees.

How to Find the Maximum Value of a Numeric Column in SQL

Problem: You’d like to find the maximum value of a numeric column. Example: Our database has a table named product with data in the following columns: id, name, year, and items. idnameyearitems 1bread roll2018345 2chocolate2017123 3butter201934 4bread roll2019456 5butter201856 6butter201778 7chocolate201987 8chocolate201876 Let’s find the maximum number of items sold over all years.

How to Find the Average of a Numeric Column in SQL

Problem: You’d like to calculate the average of numbers stored in a column. Example: Our database has a table named sale with data in the following columns: id, city, year, and amount. idcityyearamount 1Los Angeles20172345.50 2Chicago20181345.46 3Annandale2016900.56 4Annandale201723230.22 5Los Angeles201812456.20 6Chicago201789000.40 7Annandale201821005.77 8Chicago20162300.89 Let’s calculate the average sales, regardless of city or year.

How to Find the Average of a Numeric Column in SQL

Problem: You’d like to calculate the average of numbers stored in a column. Example: Our database has a table named sale with data in the following columns: id, city, year, and amount. idcityyearamount 1Los Angeles20172345.50 2Chicago20181345.46 3Annandale2016900.56 4Annandale201723230.22 5Los Angeles201812456.20 6Chicago201789000.40 7Annandale201821005.77 8Chicago20162300.89 Let’s calculate the average sales, regardless of city or year.

How to Convert a String to Uppercase in SQL

Problem: You would like to convert a string to uppercase in SQL. Example: Our database has a table named questionnaire with data in the following columns: id, first_name, last_name, and favorite_car. idfirst_namelast_namefavorite_car 1AlanJacksonHonda Civic 2ElisaThomsonTOYOTA Camry 3MaryMartinesNissan rogue 4ChrisBrownford focus 5AdamSpringRam PICKUP Our table stores the make and model of the favorite car for each person who filled out our questionnaire.

How to Use LIKE in SQL

Problem: You need to search for specific patterns (certain combinations of letters or numbers) within text data in your database. We'll show you how to use the LIKE operator in SQL to: Find city names starting with S Find city names with exactly five characters Find city names starting with S and with o as the second-to-last character You'll also learn how to use LIKE and wildcard operators in SQL to find your own patterns in text data in your database.

How to Round Up a Number to the Nearest Integer in SQL

Problem: You want to round up a number to the nearest integer in SQL. Example: Our database has a table named rent with data in the following columns: id, city, area, and bikes_for_rent. idcityareabikes_for_rent 1Los Angeles1302.151000 2Phoenix1340.69500 3Fargo126.44101 Let’s show each city’s name along with the ratio of its area to the number of bikes for rent.

How to Round Numbers in SQL

Problem: You want to round a number to a specific number of decimal places in SQL. Example: Our database has a table named product with data in the following columns: id, name, and price_net. idnameprice_net 1bread2.34 2croissant1.22 3roll0.38 Suppose there’s a tax of 24% on each product, and you’d like to compute the gross price of each item (i.e., after taxes) and round the value to two decimal places.

How to Floor Numbers in SQL

Problem: You want to round a number down to the nearest integer. Example: Our database has a table named employee with data in the following columns: id, first_name, last_name, and hours_worked (for the current month). idfirst_namelast_namehours_worked 1AlanWatson95 2LisaBlack225 3LauraWilliams104 Let’s show the first and last name of each employee along with the number of days they worked.

How to Add Rankings with DENSE_RANK() in SQL

Problem: You want to add a ranking position to rows consecutively, even if the rows have the same values. Example: Our database has a table named competition with data in the following columns: id (primary key), first_name, last_name, and score. idfirst_namelast_namescore 11JohnThomas345 14MaryJohnson222 16LisaBrown154 23AlanBlake222 32ChrisTaylor154 Let’s display all details about students: their last name, first name, and scores sorted by score in descending order.

How to Sum Values of a Column in SQL?

Problem: You’d like to sum the values of a column. Example: Our database has a table named game with data in the following columns: id, player, and score. idplayerscore 1John134 2Tom 146 3Lucy20 4Tom 118 5Tom 102 6Lucy90 7Lucy34 8John122 Let’s find the total score obtained by all players. Solution: SELECT SUM(score) as sum_score FROM game; Here’s the result:

How to Replace Part of a String in SQL

Problem: You’d like to replace part of a string with another string. Example: Our database has a table named investor with data in the following columns: id, company, and phone. idcompanyphone 1Big Market123–300-400 3The Sunny Restaurant123–222-456 4My Bank123-345-400 We’d like to change the phone number format for each company by replacing the hyphen character with a space.

How to Count the Number of Rows in a Table in SQL

Problem: You’d like to determine how many rows a table has. Example: Our database has a table named pet with data in the following columns: id, eID (electronic identifier), and name. ideIDname 123456sparky 223457mily 3NULLlessy 4NULLcarl 534545maggy Let’s count all rows in the table. Solution: COUNT(*) counts the total number of rows in the table:

How to Order by Count in SQL?

Problem: You aggregated data into groups, but you want to sort the records in descending order by the number of elements in the groups. Example: Our database has a table named user with data in the following columns: id, first_name, last_name, and country. idfirst_namelast_namecountry 1LisaWilliamsEngland 2GaryAndersPoland 3TomWilliamsPoland 4MichaelBrownFrance 5SusanSmithUSA 6AnneJonesUSA 7EllieMillerPoland Let’s create a report on our users.

How to Order By Two Columns in SQL?

Problem: You need to display records from a given table sorted by two columns. Example: Our database has a table named employee with the following columns: id, first_name, last_name, and salary. idfirst_namelast_namesalary 1LisaUlman3000 2AdaMuller2400 3ThomasGreen2400 4MichaelMuller3000 5MaryGreen2400 Let’s display all information for each employee but sort the records according to salary in descending order first and then by last name in ascending order.

How to Multiply Two Columns in SQL

Problem: You want to multiply values from two columns of a table. Example: Our database has a table named purchase with data in the following columns: id, name, price, quantity, and discount_id. idnamepricequantitydiscount_id 1pen731 2notebook582 3rubber1131 4pencil case2423 Let’s multiply the price by the quantity of the products to find out how much you paid for each item in your order.

How to Join on Multiple Columns

Problem: You want to join tables on multiple columns by using a primary compound key in one table and a foreign compound key in another. Example: Our database has three tables named student, enrollment, and payment. The student table has data in the following columns: id (primary key), first_name, and last_name. idfirst_namelast_name 1EllieWillson 2TomBrown 3SandraMiller The enrollment table has data in the following columns: primary key (student_id and course_code), is_active, and start_date.

How to Handle Divide by Zero In SQL

Problem: You want to perform division in your SQL query, but the denominator is an expression that can be zero. The database will give you an error when the denominator is in fact zero. Example: Our database has a table named investor_data with data in the following columns: id, investor_year, price_per_share, income, and expenses. idinvestor_yearprice_per_shareincomeexpenses 120162032002300 2201713020002000 3201840200100 420191559004900 Let’s divide the price per share by the difference between income and expenses to determine the P/E ratio (price-earnings ratio) for each year.

How to Find Duplicate Rows in SQL?

Problem: You have duplicate rows in your table, with only the IDs being unique. How do you find those duplicate entries? Example: Our database has a table named product with data in the following columns: id, name, and category. idnamecategory 1steakmeat 2cakesweets 3steakmeat 4porkmeat 5cakesweets 6cakesweets Let’s find duplicate names and categories of products.

How to Eliminate Duplicate Rows in SQL

Problem: You’d like to eliminate any duplicate rows from the result set of a query so that each row appears only once. Example: Our database has a table named clothes with data in the following columns: id, name, color, and year_produced. idnamecoloryear_produced 1T-shirtyellow2015 2jacketblue2016 3jeansblack2015 4jacketblue2015 5jacketgreen2016 6jacketyellow2017 7hatyellow2017 Let’s get the non-repeated names and colors of clothes produced before 2017.

How to Count Distinct Values in SQL

Problem: You’d like to count how many different non-NULL values there are in a given column. Example: Our database has a table named customer with data in the following columns: id, first_name, last_name, and city. idfirst_namelast_namecity 1JohnWilliamsChicago 2TomBrownAustin 3LucyMillerChicago 4EllieSmithDallas 5BrianJonesAustin 6AllanDavisNULL Let’s find the number of different (and non-NULL) cities.

How to Order Alphabetically in SQL

Problem: You want to display records from a table in alphabetical or reverse-alphabetical order according to given column. Example: Our database has a table named customer. The customer table contains data in the id, first_name, and last_name columns. id first_name last_name 1 Susan Thomas 2 John Michael 3 Tom Muller Let’s display each customer’s information, sorted in ascending order by their last name.

Belma Mesihovic

Grouping Data in SQL Server

People who work with data know that data grouping can sometimes be a chore. If you struggle and waste hours with Excel, OpenOffice, or some other tool trying to group various sets of data, take a look at this article and learn how to do the work much quicker and easier by using SQL. You often find yourself in a situation where you need to analyze data and present the results in a form other than the one in which the data is stored.

Dorota Wdzięczna

14 Differences Between Standard SQL and Transact-SQL

In my last article, I roughly described how standard SQL differs from T-SQL and who should learn which. Now I'd like to focus on the syntax differences and illustrate these differences with examples. If you think T-SQL is an extension implementing all the features from standard SQL, you aren't right. However, in SQL Server you will find almost all the features of the SQL standard. In this article you will find examples of some of the differences in syntax between standard SQL and Transact-SQL.

Dorota Wdzięczna

What's the Difference Between SQL and T-SQL?

If you are beginning to learn SQL and are confused by the differences between standard SQL and other similar languages like T-SQL, this article will help make things clear. You’ll not only learn about the difference between SQL and T-SQL but also find explanations concerning which topics would be better to start learning first: standard SQL or something more specific like MS SQL Server. What is Standard SQL? SQL (Structured Query Language) is a basic ANSI/ISO standard programming language designed to operate on data stored in relational databases.

Roman Pijacek

Microsoft SQL Server Pros and Cons

Thinking about using Microsoft SQL Server? If so, you’re in the right place. In this article, we’ll go over the pros and cons of Microsoft SQL Server and evaluate the platform from both a company’s and a data specialist’s perspective. What Is Microsoft SQL Server? Before diving into the pros and cons of Microsoft SQL Server, I’ll explain what it is. In technical terms, it is a relational database management system (RDBMS) developed by Microsoft.

Dorota Wdzięczna

Microsoft SQL Server 2017 Installation Step by Step

Microsoft SQL Server is one of the most popular professional database servers on the market. In this guide, I’ll show you all SQL Server 2017 installation steps to help you install it on the Windows operating system together with SQL Management Studio. If you want to learn T-SQL, the dialect of SQL used in SQL Server, check out our SQL from A to Z in MS SQL Server track.

Jeffrey J. Keller

Grouping, Rolling, and Cubing Data

The first two articles in this series highlighted SQL Server's ability to organize data into user-defined windows and its aggregate functions. Part 3 will focus on other methods of aggregating and organizing data using built-in SQL Server features – specifically, its grouping functions. For consistency, the same base data will be used as in the first two parts of this series. CREATE TABLE WindowTable (WindowID INT IDENTITY, House Varchar(32), FullName Varchar(64), PhysicalSkill Decimal(4, 2), MentalSkill Decimal (4, 2)) GO

Jeffrey J. Keller

Window Functions: Part Two: Aggregating Data

In part one of this series on SQL Server window functions, the functionality of the OVER() clause was discussed. This article will focus on aggregate functions. The majority of these can be used in conjunction with OVER. Some, like SUM() and AVG(), are widely used. Others — including VARP() and CHECKSUM_AGG() — are not as well-known, but are potentially quite useful. OVER defines the user-specified range on which a function is applied.

Jeffrey J. Keller

Window Functions in SQL Server: Part One: The OVER() Clause

Window functions were first introduced in standard SQL 2003 and then extended in SQL 2008. Since SQL Server 2005, Microsoft has been steadily improving window functions in the database engine. These functions perform an aggregate operation against a user-defined range of rows (the window) and return a detail-level value for each row. Well-known aggregate functions include SUM, AVG, MIN, MAX, and many others. Recent versions of SQL Server have introduced ranking and analytic functions such as LAG, LEAD, RANK, CUME_DIST, and many others.

Patrycja Dybka

Basic Date and Time Functions in MS SQL Server

As a follow up to our article “The Most Useful Date and Time Functions in Oracle Database”, let’s review what date and time functions look like in MS SQL Server. Let’s start with functions that extract a year, month and day from a given date. declare @dt date = '2014-10-20' select year (@dt) as year, month (@dt) as month, day (@dt) as day SQL Server uses GETDATE() and SYSDATETIME() to get a current date and time.