What is the difference between SELECT DISTINCT and GROUP BY in MySQL?-Mysql Tutorial-php.cn

What is the difference between SELECT DISTINCT and GROUP BY in MySQL?

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Release： 2023-09-18 23:53:07

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MySQL 中 SELECT DISTINCT 与 GROUP BY 的区别？

SELECT DISTINCT can be used to give different values. Use it to remove duplicate records and It can also be used with aggregate functions. For example: MAX, AVG, etc. This can be applied on a single column.

Right now, I'm creating a table to use SELECT DISTINCT on a column. Create a table Help for CREATE command -

mysql> CREATE TABLE DistinctDemo
-> (
-> id int,
-> name varchar(100)
-> );
Query OK, 0 rows affected (0.64 sec)

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Insert records −

mysql> INSERT into DistinctDemo values(1,'John');
Query OK, 1 row affected (0.17 sec)

mysql> INSERT into DistinctDemo values(2,'John');
Query OK, 1 row affected (0.18 sec)

mysql> INSERT into DistinctDemo values(3,'Bob');
Query OK, 1 row affected (0.17 sec)

mysql> INSERT into DistinctDemo values(4,'John');
Query OK, 1 row affected (0.15 sec)

mysql> INSERT into DistinctDemo values(5,'David');
Query OK, 1 row affected (0.17 sec)

mysql> INSERT into DistinctDemo values(6,'Bob');
Query OK, 1 row affected (0.16 sec)

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Display all records with the help of SELECT command. The query is as follows -

mysql> SELECT * from DistinctDemo;

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After executing the above query, we will get the following output −

+------+-------+
| id   | name  |
+------+-------+
| 1    | John  |
| 2    | John  |
| 3    | Bob   |
| 4    | John  |
| 5    | David |
| 6    | Bob   |
+------+-------+
6 rows in set (0.00 sec)

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Above, we have six records, among which John and Bob are duplicates. We can apply DISTINCT to Remove duplicate records. The syntax is as follows −

SELECT distinctcolumn_name from yourTableName order by column_name;

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Now, I am applying the above query to remove duplicates-

mysql> SELECT distinct name from DistinctDemo;

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Below is the output

+-------+
| name  |
+-------+
| John  |
| Bob   |
| David |
+-------+
3 rows in set (0.00 sec)

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Select group by can be used to get data from different columns and Group into one or more column. This can also be applied with aggregate function.For Example:SUM,AVG etc.

Firstly, I am creating a table with the CREATE command help -

column. This can also be used with aggregate functions. For example: SUM, AVG, etc.

Firstly, I am creating a table using CREATE command −

mysql> CREATE table GroupDemo1
-> (
-> id int,
-> name varchar(100),
-> address varchar(100)
-> );
Query OK, 0 rows affected (0.68 sec)

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After creating the table, I insert records into the table as shown below −

mysql> INSERT into GroupDemo1 values(1,'John','US');
Query OK, 1 row affected (0.18 sec)

mysql> INSERT into GroupDemo1 values(2,'Bob','UK');
Query OK, 1 row affected (0.13 sec)

mysql> INSERT into GroupDemo1 values(3,'David','US');
Query OK, 1 row affected (0.12 sec)

mysql> INSERT into GroupDemo1 values(4,'David','US');
Query OK, 1 row affected (0.15 sec)

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Now, we can use SELECT Command shows all records −

mysql> SELECT * from GroupDemo1;

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The following is the output-

+------+-------+---------+
| id   | name  | address |
+------+-------+---------+
| 1    | John  | US      |
| 2    | Bob   | UK      |
| 3    | David | US      |
| 4    | David | US      |
+------+-------+---------+
4 rows in set (0.00 sec)

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I will apply GROUP BY to know the number of occurrences of the same address. here it is Syntax −

SELECT column_name1,......N aggregate function( ) from yourTableName group by
column_name;

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Let us apply the above syntax to GROUP BY -

mysql> SELECT address, count(*) from GroupDemo1 group by address;

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The following is the output -

+---------+----------+
| address | count(*) |
+---------+----------+
| US      | 3        |
| UK      | 1        |
+---------+----------+
2 rows in set (0.00 sec)

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