Extract, Transform, Load with SQL on Teradata & Amazon Redshift
In this post I have shared the key differences between star schema and snowflake schema. Star schema is the most commonly used approach to design & develop data warehouse. It is simple to implement in which we have centralised one or more FACT Tables surrounded by multiple dimension tables. The fact table source keys from … Read more
I have recently changed my team and was working on a project and my business analyst asked me to CREATE A TABLE for some business logic. However when I converted the business logic into SQL I did not see it as a requirement for a new TABLE. In my opinion it should be a VIEW. … Read more
The most common method to fetch previous row value in SQL is by using the LAG function. The LAG function returns the previous row value. Depending on the order by clause the previous row is determined and the column value is returned. catid previous_catid 1 NULL 2 1 3 2 4 3 5 4 6 … Read more
Redshift SELECT Distinct is used to fetch unique rows from the table. DISTINCT is applied to all the columns mentioned in the SELECT clause and not just the first column. The example fetches DISTINCT values for one column in the table catgroup Sports Shows Concerts redshift select distinct multiple columns You can apply DISTINCT on … Read more
Duplicate rows in the table can result in data quality issues. Sometimes it is ok to have duplicate rows in the table as per business requirement. However if the duplicate rows are loaded into the table accidentally you must remove the duplicate rows. What are duplicate rows in SQL ? When the value of two … Read more