SQL Server Cheat Sheet

SQL Server is a popular relational database management system developed by Microsoft. It is widely used for storing, managing, and processing data in various environments.

Transact-SQL (T-SQL) is an extension of the SQL language, designed specifically for SQL Server. It allows for advanced database operations such as defining stored procedures, triggers, and indexes.

SQL Server Management Studio (SSMS) is the official graphical tool for managing SQL Server databases. It offers a comprehensive interface for administrators and developers to design databases, write queries, and optimize database performance, among other tasks.

Download Microsoft SQL Server here:

CREATING AND DISPLAYING DATABASES

To create a database:

CREATE DATABASE Zoo;

To list all databases on a server:

SELECT *
FROM sys.databases;

To use a specified database:

USE Zoo;

To delete a specified database:

DROP DATABASE Zoo;

To create a schema:

CREATE SCHEMA AnimalSchema;

DISPLAYING TABLES

To list all tables in a database:

SELECT *
FROM sys.tables;

To get information about a specified table:

exec sp_help 'Animal'

CREATING TABLES

To create a table:

CREATE TABLE Habitat (
  Id INT,
  Name VARCHAR(64)
);

Use IDENTITY to increment the ID automatically with each new record.

CREATE TABLE Habitat (
  Id INT PRIMARY KEY IDENTITY,
  Name VARCHAR(64)
);

To create a table with a foreign key:

CREATE TABLE Animal (
  Id INT PRIMARY KEY IDENTITY,
  Name VARCHAR(64),
  Species VARCHAR(64),
  Age INT,
  HabitatId INT,
  FOREIGN KEY (HabitatId)
    REFERENCES Habitat(Id)
);

MODIFYING TABLES

Use the ALTER TABLE or the EXEC statement to modify a table structure.

To change a table name:

EXEC sp_rename 'AnimalSchema.Animal', 'Pet'

To add a column to a table:

ALTER TABLE Animal
ADD COLUMN Name VARCHAR(64);

To change a column name:

EXEC sp_rename 'AnimalSchema.Animal.Id', 'Identifier', 'COLUMN';

To change a column data type:

ALTER TABLE Animal
ALTER COLUMN Name VARCHAR(128);

To delete a column:

ALTER TABLE Animal
DROP COLUMN Name;

To delete a table:

DROP TABLE Animal;

QUERYING DATA

To select data from a table, use the SELECT command.

An example of a single-table query:

SELECT Species, AVG(Age) AS AverageAge
FROM Animal
WHERE Id != 3
GROUP BY Species
HAVING AVG(Age) > 3
ORDER BY AVG(Age) DESC;

An example of a multiple-table query:

SELECT City.Name, Country.Name
FROM City
[INNER | LEFT | RIGHT | FULL] JOIN Country
  ON City.CountryId = Country.Id;

AGGREGATION AND GROUPING

• AVG(expr) − average value of expr for the group.
• COUNT(expr) − count of expr values within the group.
• MAX(expr) − maximum value of expr values within the group.
• MIN(expr) − minimum value of expr values within the group.
• SUM(expr) − sum of expr values within the group.

To count the rows in the table:

SELECT COUNT(*)
FROM Animal;

To count the non-NULL values in a column:

SELECT COUNT(Name)
FROM Animal;

To count unique values in a column:

SELECT COUNT(DISTINCT Name)
FROM Animal;

GROUP BY

To count the animals by species:

SELECT Species, COUNT(Id)
FROM Animal
GROUP BY Species;

To get the average, minimum, and maximum ages by habitat:

SELECT HabitatId, AVG(Age),
       MIN(Age), MAX(Age)
FROM Animal
GROUP BY HabitatId;

INSERTING DATA

To insert data into a table, use the INSERT command:

INSERT INTO Habitat VALUES (1, 'River'), (2, 'Forest');

You may specify the columns in which the data is added. The remaining columns are filled with default values or NULLs.

INSERT INTO Habitat (Name) VALUES ('Savanna');

UPDATING DATA

To update the data in a table, use the UPDATE command:

UPDATE Animal
SET
  Species = 'Duck',
  Name = 'Quack'
WHERE Id = 2;

DELETING DATA

To delete data from a table, use the DELETE command:

DELETE FROM Animal
WHERE Id = 1;

This deletes all rows satisfying the WHERE condition.

To delete all data from a table, use the TRUNCATE TABLE statement:

TRUNCATE TABLE Animal;

SQL SERVER CONVENTIONS

SELECT
 [First Name],
 [Age]
FROM [Customers];

Often, you refer to a table by its full name that consists of the schema name and the table name (for example, AnimalSchema.Habitat, sys.databases). For simplicity, we use plain table names in this cheat sheet.

THE GO SEPARATOR

In SQL Server, GO is a batch separator used to execute multiple SQL statements together. It is typically used in SQL Server Management Studio and similar tools.

TEXT FUNCTIONS

Character strings are enclosed in single quotes:

SELECT 'Michael';

Unicode strings are enclosed in single quotes and prefixed with capital N:

SELECT N'Michél';

CONCATENATION

Use the CONCAT() function to concatenate two strings:

SELECT CONCAT(N'Hi ', N'there!');
-- result: Hi there!

CONCAT() treats NULL as an empty string:

SELECT CONCAT(N'Great ', N'day', NULL);
-- result: Great day

SQL Server allows specifying a separating character (separator) using the CONCAT_WS() function. The separator is placed between the concatenated values:

SELECT CONCAT_WS(' ', 1, N'Olivier', N'Norris'); 
-- result: 1 Olivier Norris

FILTERING THE OUTPUT

To fetch the city names that are not Berlin:

SELECT Name
FROM City
WHERE Name != N'Berlin';

TEXT OPERATORS

To fetch the city names that start with a 'P' or end with an 's':

SELECT Name
FROM City
WHERE Name LIKE N'P%' OR Name LIKE N'%s';

To fetch the city names that start with any letter followed by 'ublin' (like Dublin in Ireland or Lublin in Poland):

SELECT Name
FROM City
WHERE Name LIKE N'_ublin';

OTHER USEFUL TEXT FUNCTIONS

To get the count of characters in a string:

SELECT LEN(N'LearnSQL.com'); 
-- result: 12

To convert all letters to lowercase:

SELECT LOWER(N'LEARNSQL.COM');
-- result: learnsql.com

To convert all letters to uppercase:

SELECT UPPER(N'LearnSQL.com');
-- result: LEARNSQL.COM

To get just a part of a string:

SELECT SUBSTRING(N'LearnSQL.com', 1, 5);
-- result: Learn

To replace a part of a string:

SELECT REPLACE(N'LearnSQL.com', 'SQL', 'Python');
-- result: LearnPython.com

NUMERIC FUNCTIONS

Use +, -, *, / to do some basic math.

To get the number of seconds in a week:

SELECT 60 * 60 * 24 * 7; 
-- result: 604800

In SQL Server, the division operator / performs an integer division on integer arguments. For example:

SELECT 25 / 4; 
-- result 6

To avoid the integer division, make sure at least one of the arguments is not an integer:

SELECT CAST(25 AS DECIMAL) / 4;
-- result 6.25
SELECT 25.0 / 4;
-- result 6.25

To get the remainder of a division:

SELECT MOD(13, 2); -- result: 1

To round a number to three decimal places:

SELECT ROUND(1234.56789, 3);
-- result: 1234.568

To round a number up:

SELECT CEILING(13.1), CEILING(-13.9);
-- result: 14, -13

To round the number down:

SELECT FLOOR(13.8), FLOOR(-13.2);
-- result: 13, -14

USEFUL NULL FUNCTIONS

To fetch the names of the cities whose rating values are not missing:

SELECT Name
FROM City
WHERE Rating IS NOT NULL;

COALESCE(x, y, ...)

To replace NULL in a query with something meaningful:

SELECT Domain, COALESCE(Domain, 'domain missing')
FROM Contacts;

The COALESCE() function takes any number of arguments and returns the value of the first argument that is not NULL.

NULLIF(x, y)

To save yourself from division-by-0 errors:

SELECT LastMonth, ThisMonth,
  ThisMonth * 100.0 / NULLIF(LastMonth, 0) AS BetterByPercent
FROM VideoViews;

The NULLIF(x, y) function returns NULL if x equals y, else it returns the value of x value.

DATE AND TIME

There are 6 main time-related types in MySQL:

• DATE – stores the year, month, and day in the YYYY-MM-DD format. The supported range is '0001-01-01' to '9999-12-31'.
• TIME – stores the hours, minutes, seconds, and nanoseconds in the HH:MM:SS[.nnnnnnn] format. The supported range is '00:00:00.0000000' to '23:59:59.9999999'.
• SMALLDATETIME – stores the date and time in the YYYY-MM-DD HH:MM:SS format. The supported range is '1900-01-01' to '2079-06-06'.
• DATETIME – stores the date and time in the YYYY-MM-DD HH:MM:SS[.nnn] format. The supported range is '1753-01-01' to '9999-12-31'.
• DATETIME2 – stores the date and time in the YYYY-MM-DD HH:MM:SS[.nnnnnnn] format. The supported range is '0001-01-01 00:00:00.0000000' to '9999-12-31 23:59:59.9999999'.
• DATETIMEOFFSET – stores the date and time in the YYYY-MM-DD HH:MM:SS[.nnnnnnn][+|-]hh:mm format. The supported range is '0001-01-01 00:00:00.0000000' to '9999-12-31 23:59:59.9999999' in UTC.

WHAT TIME IS IT?

To get the current datetime without the time-zone offset:

SELECT GETDATE(); 
-- result: 2023-07-27 07:21:13.937

To get the current datetime without the time-zone offset in DATETIME2 data type (higher fractional seconds precision):

SELECT SYSDATETIME(); 
-- result: 2023-07-27 07:21:13.9398213

To get the current datetime in UTC:

SELECT GETUTCDATE(); 
-- result: 2023-07-27 07:21:13.937

or in datetime2 data type (higher fractional seconds precision):

SELECT SYSUTCDATETIME(); 
-- result: 2023-07-27 07:21:13.9398213

To get the current datetime with the time-zone offset:

SELECT SYSDATETIMEOFFSET();
-- result: 2023-07-27 07:21:13.9398213 +00:00

CREATING VALUES

To create a date, time, or datetime, write the value as a string and cast it to the proper type.

SELECT CAST('2021-12-31' AS date), CAST('2021-12-31 23:59:29' AS DATETIME2);

DATE ARITHMETICS

To add or subtract from a DATE, use the DATEADD() function:

SELECT DATEADD(day, -3, '2014-04-05');
-- result: '2014-04-02'

To find the difference between two dates, use the DATEDIFF() function:

SELECT DATEDIFF(year, '2019-05-15', '2017-05-15');
-- result: -2
SELECT DATEDIFF(month, '2019-06-15', '2023-12-15');
-- result: 54

The supported date parts are: year, quarter, month, dayofyear, day, week, hour, minute, second, millisecond, microsecond, nanosecond.

EXTRACTING PARTS OF DATES

To extract a part of a date, use the functions YEAR(), MONTH(), or DAY():

SELECT YEAR(CAST('2021-12-31' AS date));
-- result: 2021

SELECT MONTH(CAST('2021-12-31' AS date));
-- result: 12

SELECT DAY(CAST('2021-12-31' AS date));
-- result: 31

You may also use the DATEPART() function:

SELECT DATEPART(year, '2013-09-15');
-- result: 2013

Supported date parts are: year, quarter, month, dayofyear, day, week, weekday, hour, minute, second, millisecond, microsecond, nanosecond, tzoffset, iso_week.

CHANGING THE TIME ZONE

Use AT TIME ZONE to convert a date and time value into a target time zone. You may use meaningful time zone names such as 'Pacific Standard Time'. SQL Server uses the names stored in the Windows Registry.

To add the target time-zone offset to a datetime value without offset information:

SELECT start_time AT TIME ZONE 'UTC';

To convert values between different time zones:

SELECT '2023-07-20 12:30:00'
  AT TIME ZONE 'UTC'
  AT TIME ZONE 'Eastern Standard Time';
-- result: 2023-07-20 08:30:00

Specify the known time-zone offset first (here, UTC) and then the time zone to which you want to convert.