Usually, we PIVOT a table using unique values extracted from a column and show the result in multiple columns.
Let us see an example.
As usual, we will use the dbo.Books table for our demo. The table has five columns and few rows in it. Hope, you have checked the above link, and created the table and inserted the rows.
Also, check this list of popular SQL Server post in our blog.
PIVOT Using Aggregate function
We will PIVOT the Books table to get the max price for each distinct category. The T-SQL aggregate MAX() function will return the maximum value from a list of values in a column.
SELECT Computers, Science, Programming, Business FROM ( SELECT Price, Category FROM dbo.Books ) Books PIVOT ( MAX(Price) FOR Category IN (Computers, Science, Programming, Business) ) Result;
Similarly, we can get the total price for each category using PIVOT and SUM() function.
SELECT Computers, Science, Programming, Business FROM ( SELECT Price, Category FROM dbo.Books ) Books PIVOT ( SUM(Price) FOR Category IN (Computers, Science, Programming, Business) ) Result;
The queries above have one similarity (other than using PIVOT), that it uses pre-defined values as column name (Computer, Science etc.). We looked for unique values in Category column and used the list in our query as columns.
Now, an obvious question comes to our mind. How do we PIVOT a table if we do not know the values for our columns? It is not always wise to hardcore values as columns. Since, categories might change in the Books table or we add new categories to the list.
PIVOT using Dynamically extracted Columns
This may also be called as Dynamic PIVOT, where values for columns are extracted dynamically using an SQL query, at runtime.
We will first extract all the Distinct categories from the table and store the result in a variable. Each value is separate by a comma.
DECLARE @Category AS VARCHAR(MAX) SELECT @Category = COALESCE(@Category + ', ', '') + CAST(Category AS VARCHAR(20)) FROM (SELECT DISTINCT Category FROM dbo.Books) Books SELECT @Category Categories
Business, Computers, Programming, Science
We got the values for our columns, all separate by a comma. Using the above result, we will now create the Dynamic PIVOT. The syntax remains the same as we did in Static PIVOT, except that we will add the variable @Columns inside the query and execute it as we execute a Stored Procedure.
DECLARE @Category AS VARCHAR(MAX) SELECT @Category = COALESCE(@Category + ', ', '') + CAST(Category AS VARCHAR(20)) FROM (SELECT DISTINCT Category FROM dbo.Books) Books DECLARE @DynamicPIVOT AS VARCHAR(MAX) SELECT @DynamicPIVOT = 'SELECT ' + @Category + ' FROM ( SELECT Price, Category FROM dbo.Books ) Books PIVOT ( MAX(Price) FOR Category IN (' + @Category + ') ) Result;' EXEC (@DynamicPIVOT)
You must use SQL Server 2005 and above to use PIVOT in your queries or procedures. SQL Server PIVOT simplifies the process of transforming data from rows to columns, where we use the row’s values as column headers. PIVOT usually works with aggregate functions, such as MAX(), SUM() etc.
Thanks for reading.
Here's a list of Top 5 popular SQL Server posts.
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