In SQL, a VIEW is a virtual table. It lets you package a complex query into a single table. We will discuss several queries in increasing difficulty to show how VIEWs can greatly simplify your work. In our examples we will introduce CROSS JOINs, Unions, the CONCAT() function, and the COALESCE() function.
SQL stands for Structured Query Language. SQL is a scripting language expected to store, control, and inquiry information put away in social databases. The main manifestation of SQL showed up in 1974, when a gathering in IBM built up the principal model of a social database. The primary business social database was discharged by Relational Software later turning out to be Oracle.
Models for SQL exist. In any case, the SQL that can be utilized on every last one of the major RDBMS today is in various flavors. This is because of two reasons:
1. The SQL order standard is genuinely intricate, and it isn’t handy to actualize the whole standard.
2. Every database seller needs an approach to separate its item from others.
Right now, contrasts are noted where fitting.
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CROSS JOIN is in the spotlight. This article finishes our small series of SQL JOIN-related publications.
SQL Server CROSS JOIN is the simplest of all joins. It implements a combination of 2 tables without a join condition. If you have 5 rows in one table and 3 rows in another, you get 15 combinations. Another definition is a Cartesian Product.
Now, why would you want to combine tables without a join condition? Hang on a bit because we are getting there. First, let’s refer to the syntax.
#sql server #cross join #inner join #outer join #sql join #sql
SQL CROSS JOIN clause is used to combine rows from two or more tables, based on a related column between them. SQL cross joins are used to join the table having no condition in which all the records of the first table comes with all the records of the second table.
Cross join is also called a Cartesian product.
Unlike an INNER JOIN or LEFT JOIN, the cross join does not establish the relationship between the joined tables. When each row of the first table is combined with each row from the second table, known as Cartesian join or cross join.
The CROSS JOIN joined every row from the first table (T1) with every row from the second table (T2).
In other words, the cross join returns the Cartesian product of rows from both the tables. The number of rows in a Cartesian product is the product of the number of rows in each involved tables.
#sql #sql cross join #inner join
This article will introduce the concept of SQL recursive. Recursive CTE is a really cool. We will see that it can often simplify our code, and avoid a cascade of SQL queries!
The recursive queries are used to query hierarchical data. It avoids a cascade of SQL queries, you can only do one query to retrieve the hierarchical data.
First, what is a CTE? A CTE (Common Table Expression) is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. For example, you can use CTE when, in a query, you will use the same subquery more than once.
A recursive CTE is one having a subquery that refers to its own name!
Recursive CTE is defined in the SQL standard.
A recursive CTE has this structure:
In this example, we use hierarchical data. Each row can have zero or one parent. And it parent can also have a parent etc.
Create table test (id integer, parent_id integer); insert into test (id, parent_id) values (1, null); insert into test (id, parent_id) values (11, 1); insert into test (id, parent_id) values (111, 11); insert into test (id, parent_id) values (112, 11); insert into test (id, parent_id) values (12, 1); insert into test (id, parent_id) values (121, 12);
For example, the row with id 111 has as ancestors: 11 and 1.
Before knowing the recursive CTE, I was doing several queries to get all the ancestors of a row.
For example, to retrieve all the ancestors of the row with id 111.
While (has parent) Select id, parent_id from test where id = X
With recursive CTE, we can retrieve all ancestors of a row with only one SQL query :)
WITH RECURSIVE cte_test AS ( SELECT id, parent_id FROM test WHERE id = 111 UNION SELECT test.id, test.parent_id FROM test JOIN cte_test ON cte_test.id = test.parent_id
) SELECT * FROM cte_test
It indicates we will make recursive
It is the initial query.
It is the recursive expression! We make a jointure with the current CTE!
Replay this example here
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When you develop large chunks of T-SQL code with the help of the SQL Server Management Studio tool, it is essential to test the “Live” behavior of your code by making sure that each small piece of code works fine and being able to allocate any error message that may cause a failure within that code.
The easiest way to perform that would be to use the T-SQL debugger feature, which used to be built-in over the SQL Server Management Studio tool. But since the T-SQL debugger feature was removed completely from SQL Server Management Studio 18 and later editions, we need a replacement for that feature. This is because we cannot keep using the old versions of SSMS just to support the T-SQL Debugger feature without “enjoying” the new features and bug fixes that are released in the new SSMS versions.
If you plan to wait for SSMS to bring back the T-SQL Debugger feature, vote in the Put Debugger back into SSMS 18 to ask Microsoft to reintroduce it.
As for me, I searched for an alternative tool for a T-SQL Debugger SSMS built-in feature and found that Devart company rolled out a new T-SQL Debugger feature to version 6.4 of SQL – Complete tool. SQL Complete is an add-in for Visual Studio and SSMS that offers scripts autocompletion capabilities, which help develop and debug your SQL database project.
The SQL Debugger feature of SQL Complete allows you to check the execution of your scripts, procedures, functions, and triggers step by step by adding breakpoints to the lines where you plan to start, suspend, evaluate, step through, and then to continue the execution of your script.
You can download SQL Complete from the dbForge Download page and install it on your machine using a straight-forward installation wizard. The wizard will ask you to specify the installation path for the SQL Complete tool and the versions of SSMS and Visual Studio that you plan to install the SQL Complete on, as an add-in, from the versions that are installed on your machine, as shown below:
Once SQL Complete is fully installed on your machine, the dbForge SQL Complete installation wizard will notify you of whether the installation was completed successfully or the wizard faced any specific issue that you can troubleshoot and fix easily. If there are no issues, the wizard will provide you with an option to open the SSMS tool and start using the SQL Complete tool, as displayed below:
When you open SSMS, you will see a new “Debug” tools menu, under which you can navigate the SQL Debugger feature options. Besides, you will see a list of icons that will be used to control the debug mode of the T-SQL query at the leftmost side of the SSMS tool. If you cannot see the list, you can go to View -> Toolbars -> Debugger to make these icons visible.
During the debugging session, the SQL Debugger icons will be as follows:
The functionality of these icons within the SQL Debugger can be summarized as:
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