What is the difference between SELECT DISTINCT and GROUP BY in MySQL?
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)
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)
Display all records with the help of SELECT command. The query is as follows -
mysql> SELECT * from DistinctDemo;
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)
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;
Now, I am applying the above query to remove duplicates-
mysql> SELECT distinct name from DistinctDemo;
Below is the output
+-------+ | name | +-------+ | John | | Bob | | David | +-------+ 3 rows in set (0.00 sec)
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)
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)
Now, we can use SELECT Command shows all records −
mysql> SELECT * from GroupDemo1;
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)
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;
Let us apply the above syntax to GROUP BY -
mysql> SELECT address, count(*) from GroupDemo1 group by address;
The following is the output -
+---------+----------+ | address | count(*) | +---------+----------+ | US | 3 | | UK | 1 | +---------+----------+ 2 rows in set (0.00 sec)
The above is the detailed content of What is the difference between SELECT DISTINCT and GROUP BY in MySQL?. For more information, please follow other related articles on the PHP Chinese website!
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