Can You Group By An Alias In Sql

Ava Flores
• Sunday, 29 November, 2020
• 8 min read

For most relational database systems, this order explains which names (columns or aliases) are valid because they must have been introduced in a previous step. There are exceptions though: MySQL and Postgres seem to have additional smartness that allows it.

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Of course this starts to be a pain if you are doing this interactively and you edit the query to change the number or order of columns in the result. SQL Server doesn't allow you to reference the alias in the GROUP BY clause because of the logical order of processing.

I'm not answering why it is so, but only wanted to show a way around that limitation in SQL Server by using CROSS APPLY to create the alias. Caution that using alias in the Group By (for services that support it, such as Postgres) can have unintended results.

For example, if you create an alias that already exists in the inner statement, the Group By will chose the inner field name. I avoid ordinal position notation as recommended by Bill for reasons documented in this SO question.

The easy and robust alternative is to always repeat the expression in the GROUP BY clause. Beware of using aliases when grouping the results from a view in SQLite.

Back in the day I found that RDB, the former DEC product now supported by Oracle allowed the column alias to be used in the GROUP BY. Mainstream Oracle through version 11 does not allow the column alias to be used in the GROUP BY.

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In at least Postgres, toucan use the alias name in the group by clause: I wouldn't recommend renaming an alias as a change in capitalization, that causes confusion.

This technique applies in a straightforward way to your “edit” scenario: Unfortunately toucan 't reference your alias in the GROUP BY statement, you'll have to write the logic again, amazing as that seems.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges For anyone who finds themselves with the following problem (grouping by ensuring zero and null values are treated as equals)...

(I.e. SQL Server complains that you haven't included the field Amount in your Group By or aggregate function) ...remember to place the exact same function in your SELECT...

Answered Jul 19, 2019by Son Kumar (40.3k points)In SQL, to fetch the result set the queries will be executed in the following order: In most of the DBMS, this order explains which names (columns or aliases) are valid because they must have been introduced in the previous step.

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Therefore, in SQL Server and Oracle, you cannot use the term in the GROUP BY clause that you have defined in the SELECT clause because the GROUP BY is executed before the SELECT clause. Making statements based on opinion; back them up with references or personal experience.

Summary : in this tutorial, you will learn how to use Subgroup BY clause to group rows based on one or more columns. Grouping is one of the most important tasks that you have to deal with while working with the databases.

The GROUP BY clause is an optional clause of the SELECT statement that combines rows into groups based on matching values in specified columns. It is not mandatory to include an aggregate function in the SELECT clause.

However, if you use an aggregate function, it will calculate the summary value for each group. We will use the employees and departments tables in the sample database to demonstrate how the GROUP BY clause works.

For example, in the shipping department, there are 2 employees holding the shipping clerk job, 1 employee holding the stock clerk job, and 4 employees holding the stock manager job. The following statement also retrieves the phone numbers but instead of using the GROUP BY clause, it uses the DISTINCT operator.

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The result set is the same except that the one returned by the DISTINCT operator is not sorted. It’s a name you give to a column or a table in your SQL query to make it easier to display the results or to write your query.

SQL aliases are a useful feature and are available in all major database vendors, including Oracle, SQL Server, MySQL, PostgreSQL. The SQL AS keyword is used to define a column alias.

This query gives an alias of annual_salary to the salary column. Readers of your query may ask themselves if you are missing a comma by accident or adding a column alias deliberately, making it confusing for the reader.

Looking at this query, it’s not easy to see if the comma was forgotten, or if it was written to use an alias of start_date for the hire_date column. This SQL can be used to set up the sample data used in this guide.

LAST_NAMEHIRE_DATE SMITH1 Feb 2018ANDERSON14 Sep 2012JONES20 Nov 2015The column shown as hire_date above is actually stored as hit in the table. This example uses an expression and gives it a column alias.

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FIRST_NAMELAST_NAMEFULL_NAME JOHNSMITHJOHN SMITHSALLYANDERSONSALLY ANDERSONMARKJONESMARK Jones names are concatenated into a single field, which is called full_name. LAST_NAMEHIRE_DATETENURE_MONTHS SMITH1 Feb 201815ANDERSON14 Sep 201279JONES20 Nov 201541This tenure_months column shows the number of months an employee has been working for.

If you ’re performing complicated logic but want to do further operations on it, it’s often a good idea to enclose it in a subquery. This query uses the tenure_months, calculated from the subquery, in the outer query as both a column to display and an input into the CASE statement.

It’s a short name you give to a table when you use it in an SQL query. Improving the readability of queries Speeding up the autocomplete feature in your SQL IDE.

Allowing you to use two instances of the same table (for queries using a self join, for example) Most of the aliases I use and see in other people’s code are one to three letters long.

If you don’t use the AS keyword, there is no risk of tables being excluded. You ’ll likely get a syntax error when you run the query, instead of a column missing in your output.

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Also, on Oracle SQL, you ’ll get an error if you add the AS keyword to the table alias. Using a table alias also makes it easier to use the autocomplete feature of most IDEs.

In an IDE, to add a column into the SELECT statement, you ’ll need to type out the full name of the column. Notice that the table aliases have been used as a prefix to the column names in the SELECT clause.

This is optional in many cases but is often required (if there are two tables with the same column name). It also helps to clarify which table a column exists in.

LAST_NAMESALARY SMITH40000ANDERSON60000JONES45000 This example demonstrates how to use a table alias as part of the WHERE clause. This is done using the SQL AS keyword, which is an optional keyword in many SQL statements including SELECT, UPDATE, and DELETE.

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