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Sometimes, in the quest for raw SQL performance, you are forced to sacrifice legibility and maintainability of your code, unless you then document your code lavishly. Phil Factor's SQL Speed Phreak challenge produced some memorable code, but can SQL features introduced since then help to produce code that performs as well and is also easy to understand? Kathi Kellenberger investigates.

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Code coverage is a practice that goes hand in hand with automated testing, reporting the percentage of your code that has been exercised during a test run. Ed Elliott and Redgate have partnered to make a code coverage tool available for SQL Server, both free and open source. SQL Cover measures the coverage of your SQL Server stored procedures and functions. It has built-in support for the popular tSQLt unit testing framework, but can also be used alongside any automated testing framework of your choosing. Find out more in this blog post.

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Question of the Day

The string_agg function

We create the following table and then insert some records in it:

create table t1 (
   id int primary key,
   category char(1) not null,
   product varchar(50)
);

insert into t1 values
(1, 'A', 'Product 1'),
(2, 'A', 'Product 2'),
(3, 'A', 'Product 3'),
(4, 'B', 'Product 4'),
(5, 'B', 'Product 5');
What happens if we execute the following query in both Sql Server and PostgreSQL?
select id, 
category, 
string_agg(product, ';')
                 over (partition by category order by id
                 rows between unbounded preceding and unbounded following) as stragg
from t1;

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