What is distinct in sql

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Verbal Ability. Interview Questions. Firefox is using Microsoft Access in our examples. Select all the different values from the Country column in the Customers table. We just launched W3Schools videos. Get certified by completing a course today!

A sort distinct operator takes the 6 unique values as input and comes up with 4 unique combinations as output. One more simple example on distinct columns. Why is this result happening? The fact is that each record represents a unique name of animal breeding.

Therefore, we have six unique records. The Transact SQL language is just like any other computer language that humans have built. There are two phases to processing a program written in a given language. The first phase is called the lexical analyzer. The purpose of this phase it to see if the code is syntactically correct.

The second phase is the parser for either a compiler or an interpreter. For instance, the C language compiles the a given program into assembly object code. It does not actual execute the program.

The BASIC language which is an interpreter will execute the program line by line until a end of program is found. I did a lot of programming in these languages in the s. The final answer is the fact that Transact SQL is a domain specific language which is interpreted by the database engine. With any language, the designer has to come up with a set of rules.

Of course, the optimizer that creates the execution plan might actually change the order if necessary. The image below is taken from the MSDN webpage.

To recap, a solid understanding of the execution order of a SELECT statement is valuable when trying to optimize query plans. Today, we have seen both SQL statements execute in the same amount of time. There will be times in which two statements will return the same results but with widely different execution times. The simple PETS dataset was manually created by this author.

However, there are animal shelters that might have similar data. They might want to know the average age of a given pet. Does the following T-SQL generate the same results? The image below shows two different averages.

Therefore, the results are not the same. We have two animals that are exactly 4 years old. See why it is worth learning in and why you should choose our SQL courses to do so. What Is Data Engineering? Read this article to find out. Data Types in SQL. Take 5 minutes to learn about all the data types in SQL.