SQL에서 GROUP BY와 ORDER BY의 차이점은 무엇입니까

SQL에서 GROUP BY와 ORDER BY의 차이점은 무엇입니까

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일반적으로 어느 것을 사용합니까? 예를 적극 권장합니다!

MySql을 언급하고 있지만 다른 DBMS와는 다른 개념을 상상할 수 없습니다.

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ORDER BY는 품목 반품 순서를 변경합니다.

GROUP BY는 그룹화되지 않은 열 (예 : SUM, COUNT, AVG 등)에서 집계 기능을 수행 할 수 있도록 지정된 열을 기준으로 레코드를 집계합니다.

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ORDER BY는 품목 반품 순서를 변경합니다.

GROUP BY는 그룹화되지 않은 열 (예 : SUM, COUNT, AVG 등)에서 집계 기능을 수행 할 수 있도록 지정된 열을 기준으로 레코드를 집계합니다.

TABLE:
ID NAME
1  Peter
2  John
3  Greg
4  Peter

SELECT *
FROM TABLE
ORDER BY NAME

= 
3 Greg
2 John
1 Peter
4 Peter

SELECT Count(ID), NAME
FROM TABLE
GROUP BY NAME

= 
1 Greg
1 John 
2 Peter

SELECT NAME
FROM TABLE
GROUP BY NAME
HAVING Count(ID) > 1

=
Peter

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순서 : 데이터를 오름차순 또는 내림차순으로 정렬합니다.

CUSTOMERS 테이블을 고려하십시오 .

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

다음은 NAME별로 결과를 오름차순으로 정렬하는 예입니다.

SQL> SELECT * FROM CUSTOMERS
     ORDER BY NAME;

결과는 다음과 같습니다.

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
+----+----------+-----+-----------+----------+

GROUP BY : 동일한 데이터를 그룹으로 정렬합니다.

이제 CUSTOMERS 테이블에는 이름이 중복 된 다음 레코드가 있습니다.

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Ramesh   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | kaushik  |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

if you want to group identical names into single name, then GROUP BY query would be as follows:

SQL> SELECT * FROM CUSTOMERS
     GROUP BY NAME;

This would produce the following result: (for identical names it would pick the last one and finally sort the column in ascending order)

    +----+----------+-----+-----------+----------+   
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  4 | kaushik  |  25 | Mumbai    |  6500.00 |
    |  6 | Komal    |  22 | MP        |  4500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    |  2 | Ramesh   |  25 | Delhi     |  1500.00 |
    +----+----------+-----+-----------+----------+

as you have inferred that it is of no use without SQL functions like sum,avg etc..

so go through this definition to understand the proper use of GROUP BY:

A GROUP BY clause works on the rows returned by a query by summarizing identical rows into a single/distinct group and returns a single row with the summary for each group, by using appropriate Aggregate function in the SELECT list, like COUNT(), SUM(), MIN(), MAX(), AVG(), etc.

Now, if you want to know the total amount of salary on each customer(name), then GROUP BY query would be as follows:

SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS
     GROUP BY NAME;

This would produce the following result: (sum of the salaries of identical names and sort the NAME column after removing identical names)

+---------+-------------+
| NAME    | SUM(SALARY) |
+---------+-------------+
| Hardik  |     8500.00 |
| kaushik |     8500.00 |
| Komal   |     4500.00 |
| Muffy   |    10000.00 |
| Ramesh  |     3500.00 |
+---------+-------------+

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The difference is exactly what the name implies: a group by performs a grouping operation, and an order by sorts.

If you do SELECT * FROM Customers ORDER BY Name then you get the result list sorted by the customers name.

If you do SELECT IsActive, COUNT(*) FROM Customers GROUP BY IsActive you get a count of active and inactive customers. The group by aggregated the results based on the field you specified.

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They have totally different meaning and aren't really related at all.

ORDER BY allows you to sort the result set according to different criteria, such as first sort by name from a-z, then sort by the price highest to lowest.

(ORDER BY name, price DESC)

GROUP BY allows you to take your result set, group it into logical groups and then run aggregate queries on those groups. You could for instance select all employees, group them by their workplace location and calculate the average salary of all employees of each workplace location.

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Simple, ORDER BY orders the data and GROUP BY groups, or combines the data.

ORDER BY orders the result set as per the mentioned field, by default in ascending order.

Suppose you are firing a query as ORDER BY (student_roll_number), it will show you result in ascending order of student's roll numbers. Here, student_roll_number entry might occur more than once.

In GROUP BY case, we use this with aggregate functions, and it groups the data as per the aggregate function, and we get the result. Here, if our query has SUM (marks) along with GROUP BY (student_first_name) it will show the sum of marks of students belonging to each group (where all members of a group will have the same first name).

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GROUP BY is used to group rows in a select, usually when aggregating rows (e.g. calculating totals, averages, etc. for a set of rows with the same values for some fields).

ORDER BY is used to order the rows resulted from a select statement.

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Some good examples there. Just like to add my own from webcheatsheet which gives good clear examples, as well as letting you execute your own SQL.

SQL Order By

SQL Group By

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ORDER BY shows a field in ascending or descending order. While GROUP BY shows same fieldnames, id's etc in only one output.

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1. GROUP BY will aggregate records by the specified column which allows you to perform aggregation functions on non-grouped columns (such as SUM, COUNT, AVG, etc.). ORDER BY alters the order in which items are returned.
2. If you do SELECT IsActive, COUNT(*) FROM Customers GROUP BY IsActive you get a count of active and inactive customers. The group by aggregated the results based on the field you specified. If you do SELECT * FROM Customers ORDER BY Name then you get the result list sorted by the customer’s name.
3. If you GROUP, the results are not necessarily sorted; although in many cases they may come out in an intuitive order, that's not guaranteed by the GROUP clause. If you want your groups sorted, always use an explicitly ORDER BY after the GROUP BY.
4. Grouped data cannot be filtered by WHERE clause. Order data can be filtered by WHERE clause.

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It should be noted GROUP BY is not always necessary as (at least in PostgreSQL, and likely in other SQL variants) you can use ORDER BY with a list and you can still use ASC or DESC per column...

SELECT name_first, name_last, dob 
FROM those_guys 
ORDER BY name_last ASC, name_first ASC, dob DESC;

참고URL : https://stackoverflow.com/questions/1277460/what-is-the-difference-between-group-by-and-order-by-in-sql