Sql-Interview

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

Consider the following code:

USE tempdb;
GO

DROP TABLE IF EXISTS dbo.Customers;
GO

CREATE TABLE dbo.Customers
(
    CustomerID int IDENTITY(1,1)
        CONSTRAINT PK_dbo_Customers PRIMARY KEY,
    TradingName nvarchar(100) NOT NULL,
    CreatedDate AS SYSDATETIME()
);
GO

INSERT dbo.Customers (TradingName)
VALUES (N'Customer A');
GO

SELECT * FROM dbo.Customers;
GO
SELECT * FROM dbo.Customers;
GO

Will the CreatedDate column return the same value in both SELECT statements?

2021-04-13

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Security Level: Intro

Question:

Many applications connect to SQL Server databases with users that are members of the db_datareader and/or db_datawriter roles?

Why should you avoid using those roles?

Answer:

db_datareader and db_datawriter are fixed database roles that were provided for convenience. They aren’t a good option from a security perspective.

2021-04-09

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Intro

Question:

Many versions of SQL require every SQL statement to be terminated with a semicolon.

Since it was created, T-SQL has listed statement terminators as optional.

Are there any situations where they are required, and not optional?

2021-04-08

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Intro

Question:

Look at the following multi-row INSERT statement:

INSERT Sales.CustomerGroups
(
    CustomerGroupID, CustomerGroupName
)
VALUES (1, 'Group A'),
       (2, NULL),
       (3, 'Group C');

The column CustomerGroupName is defined as NOT NULL so the second row cannot be inserted.

2021-04-06

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Intro

Question:

If you create a table using the following code, what would the name of the primary key constraint look like?

CREATE TABLE Sales.CustomerGroups
(
    CustomerGroupID int IDENTITY(1, 1) PRIMARY KEY,
    CustomerGroupName nvarchar(50) NOT NULL
);

How could you specify the name?

2021-04-01

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

When you are writing an INSERT statement in T-SQL, the column list is usually optional.

Why would including it be a good idea? When would it ever be required (i.e. not optional)?

Answer:

2021-03-30

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Query Performance Level: Medium

Question:

In SQL Server a column that is defined with a bit data type can only have the values 0, or 1, or it can be NULL if the column allows it.

Given such a small number of possible values, are bit columns ever useful in indexes? Can you give an example of when they might or might not be useful?

2021-03-26

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

When you are writing a CREATE TABLE statement to define a new table, after each column, you can write NULL or NOT NULL, but doing that is optional.

Why is it a good practice to include it, and what happens if you leave it out? Are the columns defined as NULL or as NOT NULL? Are there any exceptions to this?

2021-03-25

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Security Level: Medium

Question:

I have an application that connects to the database as a user called ReaderApp. The only role that ReaderApp has been added to is db_datareader. The application was previously only using SELECT statements to read data that was required.

2021-03-19

Many clients hire me to carry out job interviews on their behalf. If they’re hiring someone for a data-related role, they want to make sure they’re hiring the right person. That usually means two things:

• The person will fit well within the culture of the organization
• The person is technically competent.

I can’t help with the first one. If I’ve worked with the client for a long time, I might have a pretty good idea but ultimately, that’s something the client needs to decide.

2021-03-18