In SQL often we need to merge records from a source table to a target table. The source table could be a staging table where the source system sent new & updated records to be reconciled with the a target table. Let’s look at an example as to how to...

Let’s look at a standard teams interview question to understand your SQL knowledge in using a non-equi join. Problem Statement 1 Given the below 5 teams

1) Write a query so that each team plays with each other only once. 2) Write a query so that each team plays...

Here is another SQL scenario based interview question to determine a candidate’s ability to translate a business requirement into an SQL query. Problem Statement Given the below data of running account balance, find the start_date and end_date where the balance changes.

Expected output:

Create sample data

Solution...

Here is another SQL scenario based interview question to determine a candidate’s ability to translate a business requirement into an SQL query. These are scenarios where you want to find a value at a certain point in time. Lean more about SCD Type 2 at 13 Data Warehouse interview Q&As...

Let’s look at a very common problem statement of finding out the repeat customers, repeat visits, etc. The key to this problem is first determining the first visit or first purchase and then comparing it with the remaining records. Problem Statement 1 Given the below table, how will you determine...

We all know how to get a distinct count of a column. It can be done with COUNT(DISTINCT column_name). For example:

Outputs:

In this post let’s look at various approaches to count unique values. Using DISTINCT, … Read more ›...

This extends Common Table Expressions (i.e. CTE) in SQL using the “WITH” clause. You can try the example on DB Fiddle. Use MySQL v8.0 or later. Scenario: 1 Given a table like this with each entry with two dates (i.e. from_date & … Read more ›...