SQL Cheatsheet

Code snippets for common tasks with SQL Server and SQL Express

Contents

Mostly applies to SQL Server and SQL Express

Log Into Instance

#sqlcmd -S <YOUR DATABASE NAME> -E
sqlcmd -S localhost\SQLEXPRESS -E

Instance Level Operations

List Instance Databases

SELECT [name] FROM [master].[dbo].[sysdatabases]
GO

Create Database

CREATE DATABASE [TestDatabase]
GO

Drop Database

DROP DATABASE TestDatabase
GO

Database Level Operations

List Database Tables

SELECT [TABLE_NAME]
FROM [TestDatabase].[INFORMATION_SCHEMA].[TABLES]
WHERE [TABLE_TYPE] = 'BASE TABLE'
GO

List Columns in Table

SELECT * FROM [TestDatabase].[INFORMATION_SCHEMA].[COLUMNS]
 WHERE [TABLE_NAME] = 'Persons'
GO

Create Table

CREATE TABLE [TestDatabase].[dbo].[Persons] (
    PersonId int,
    LastName varchar(255),
    FirstName varchar(255),
    Address varchar(255),
    City varchar(255)
)
GO

Update Column Data Type

ALTER Table [TestDatabase].[dbo].[Persons]
    ALTER COLUMN [PersonId] int NOT NULL
GO

Add Column Constraint

ALTER Table [TestDatabase].[dbo].[Persons]
    ADD CONSTRAINT PK_Person PRIMARY KEY ([PersonId])
GO
CREATE TABLE [TestDatabase].[dbo].[Items]
   (
      ItemId int NOT NULL, 
      PersonId int NOT NULL, 
      Name nvarchar(50),
      CONSTRAINT PK_Items PRIMARY KEY (ItemId),
      CONSTRAINT FK_Items_Person FOREIGN KEY ([PersonId])
      REFERENCES [Persons] ([PersonId])
   )
GO

Drop Table

DROP TABLE [Persons]
GO

Insert Item into Table

INSERT INTO [TestDatabase].[dbo].[Persons]
    ([PersonId], [LastName], [FirstName], [Address], [City])
VALUES (1, 'Name', 'Surname', 'Home', 'Place')
GO

Retrieve Table Values

We can retrieve all values from a table with:

SELECT TOP (10) [PersonId]
      ,[LastName]
      ,[FirstName]
      ,[Address]
      ,[City]
  FROM [TestDatabase].[dbo].[Persons]
GO

We can get a specific set of values with a condition

SELECT *
FROM [TestDatabase].[dbo].[Persons]
WHERE [FirstName] = 'John'

Or search for a pattern in a field with LIKE:

SELECT *
FROM [TestDatabase].[dbo].[Persons]
WHERE [FirstName] LIKE '%John%'

Update Table Item

UPDATE [TestDatabase].[dbo].[Persons]
SET [FirstName] = 'John', [LastName] = 'Smith'
WHERE [PersonId] = 1
GO

Testing Statements

When running SQL queries it may sometimes be necessary to check if your query will work as expected before you actually run it you can wrap your query in:

BEGIN TRANSACTION
    ... DO STUFF
ROLLBACK

ROLLBACK will roll back to the DB status before the query was carried out

And once you have verified that the query did what you expected, you can change the ROLLBACK to COMMIT

BEGIN TRANSACTION
    ... DO STUFF
COMMIT

We can test a deletion of a Person and view the result with:

BEGIN TRANSACTION

SELECT * FROM [TestDatabase].[dbo].[Persons]

DELETE FROM [TestDatabase].[dbo].[Persons] 
    WHERE [LastName] = 'Person2'

SELECT * FROM [TestDatabase].[dbo].[Persons]

ROLLBACK

And we can then COMMIT this when we are sure it works

BEGIN TRANSACTION

SELECT * FROM [TestDatabase].[dbo].[Persons]

DELETE FROM [TestDatabase].[dbo].[Persons] 
    WHERE [LastName] = 'Person2'

SELECT * FROM [TestDatabase].[dbo].[Persons]

COMMIT

Table Joining

Inner Join

To use an Inner Join based on two tables we can use the INNER JOIN keywords and then get the fields from the tables we want to use for our output table:

SELECT
a.FirstName as FirstName,
a.Email as Email,
a.ID as ID,

b.Vehicle as Vehicle,
b.Registered as IsRegistered

FROM Table_1 as a 
INNER JOIN Table_2 as b
ON a.ID = b.UserId