MySQL select one column DISTINCT, with corresponding other columns

The Question :

203 people think this question is useful
ID   FirstName   LastName
1      John        Doe
2      Bugs        Bunny
3      John        Johnson

I want to select DISTINCT results from the FirstName column, but I need the corresponding ID and LastName.

The result set needs to show only one John, but with an ID of 1 and a LastName of Doe.

The Question Comments :
  • You want the last name belonging to the lowest ID with a distinct first name?
  • What is the logic that should go into the selection of the top one? I would think you would want both John Doe and John Johnson to show up since they are two distinct Johns but that is just me.
  • DISTINCT is not a function. All answers with DISTINCT() are wrong. The error will show up when you do not place it after SELECT.
  • ALL answers using parentheses after the word distinct are indeed wrong. Distinct is NOT a function so it cannot accept a parameter. The parentheses following distinct are simply ignored. Unless you are using PostgreSQL where the parentheses will form a “complex data type”

The Answer 1

204 people think this answer is useful

try this query

 SELECT ID, FirstName, LastName FROM table GROUP BY(FirstName)

The Answer 2

66 people think this answer is useful

The DISTINCT keyword doesn’t really work the way you’re expecting it to. When you use SELECT DISTINCT col1, col2, col3 you are in fact selecting all unique {col1, col2, col3} tuples.

The Answer 3

65 people think this answer is useful

To avoid potentially unexpected results when using GROUP BY without an aggregate function, as is used in the accepted answer, because MySQL is free to retrieve ANY value within the data set being grouped when not using an aggregate function [sic] and issues with ONLY_FULL_GROUP_BY. Please consider using an exclusion join.

Exclusion Join – Unambiguous Entities

Assuming the firstname and lastname are uniquely indexed (unambiguous), an alternative to GROUP BY is to sort using a LEFT JOIN to filter the result set, otherwise known as an exclusion JOIN.

See Demonstration

Ascending order (A-Z)

To retrieve the distinct firstname ordered by lastname from A-Z

Query

SELECT t1.*
FROM table_name AS t1
LEFT JOIN table_name AS t2
ON t1.firstname = t2.firstname
AND t1.lastname > t2.lastname
WHERE t2.id IS NULL;

Result

| id | firstname | lastname |
|----|-----------|----------|
|  2 |      Bugs |    Bunny |
|  1 |      John |      Doe |

Descending order (Z-A)

To retrieve the distinct firstname ordered by lastname from Z-A

Query

SELECT t1.*
FROM table_name AS t1
LEFT JOIN table_name AS t2
ON t1.firstname = t2.firstname
AND t1.lastname < t2.lastname
WHERE t2.id IS NULL;

Result

| id | firstname | lastname |
|----|-----------|----------|
|  2 |      Bugs |    Bunny |
|  3 |      John |  Johnson |

You can then order the resulting data as desired.


Exclusion Join – Ambiguous Entities

If the first and last name combination are not unique (ambiguous) and you have multiple rows of the same values, you can filter the result set by including an OR condition on the JOIN criteria to also filter by id.

See Demonstration

table_name data

(1, 'John', 'Doe'),
(2, 'Bugs', 'Bunny'),
(3, 'John', 'Johnson'),
(4, 'John', 'Doe'),
(5, 'John', 'Johnson')

Query

SELECT t1.*
FROM table_name AS t1
LEFT JOIN table_name AS t2
ON t1.firstname = t2.firstname
AND (t1.lastname > t2.lastname
OR (t1.firstname = t1.firstname AND t1.lastname = t2.lastname AND t1.id > t2.id))
WHERE t2.id IS NULL;

Result

| id | firstname | lastname |
|----|-----------|----------|
|  1 |      John |      Doe |
|  2 |      Bugs |    Bunny |


Ordered Subquery

EDIT

My original answer using an ordered subquery, was written prior to MySQL 5.7.5, which is no longer applicable, due to the changes with ONLY_FULL_GROUP_BY. Please use the exclusion join examples above instead.

It is also important to note; when ONLY_FULL_GROUP_BY is disabled (original behavior prior to MySQL 5.7.5), the use of GROUP BY without an aggregate function may yield unexpected results, because MySQL is free to choose ANY value within the data set being grouped [sic].

Meaning an ID or lastname value may be retrieved that is not associated with the retrieved firstname row.


WARNING

With MySQL GROUP BY may not yield the expected results when used with ORDER BY

See Test Case Example

The best method of implementation, to ensure expected results, is to filter the result set scope using an ordered subquery.

table_name data

(1, 'John', 'Doe'),
(2, 'Bugs', 'Bunny'),
(3, 'John', 'Johnson')

Query

SELECT * FROM (
    SELECT * FROM table_name ORDER BY ID DESC
) AS t1
GROUP BY FirstName

Result

| ID | first |    last |
|----|-------|---------|
|  2 |  Bugs |   Bunny |
|  3 |  John | Johnson |


Comparison

To demonstrate the unexpected results when using GROUP BY in combination with ORDER BY

Query

SELECT * FROM table_name GROUP BY FirstName ORDER BY ID DESC

Result

| ID | first |  last |
|----|-------|-------|
|  2 |  Bugs | Bunny |
|  1 |  John |   Doe |

The Answer 4

24 people think this answer is useful
SELECT ID,LastName 
From TABLE_NAME 
GROUP BY FirstName 
HAVING COUNT(*) >=1

The Answer 5

4 people think this answer is useful
SELECT firstName, ID, LastName from tableName GROUP BY firstName

The Answer 6

4 people think this answer is useful

How about

`SELECT 
    my_distinct_column,
    max(col1),
    max(col2),
    max(col3)
    ...
 FROM
    my_table 
 GROUP BY 
    my_distinct_column`

The Answer 7

2 people think this answer is useful

Not sure if you can do this with MySQL, but you can use a CTE in T-SQL

; WITH tmpPeople AS (
 SELECT 
   DISTINCT(FirstName),
   MIN(Id)      
 FROM People
)
SELECT
 tP.Id,
 tP.FirstName,
 P.LastName
FROM tmpPeople tP
JOIN People P ON tP.Id = P.Id

Otherwise you might have to use a temporary table.

The Answer 8

2 people think this answer is useful

As pointed out by fyrye, the accepted answer pertains to older versions of MySQL in which ONLY_FULL_GROUP_BY had not yet been introduced. With MySQL 8.0.17 (used in this example), unless you disable ONLY_FULL_GROUP_BY you would get the following error message:

mysql> SELECT id, firstName, lastName FROM table_name GROUP BY firstName;

ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column ‘mydatabase.table_name.id’ which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

One way to work around this not mentioned by fyrye, but described in https://dev.mysql.com/doc/refman/5.7/en/group-by-handling.html, is to apply the ANY_VALUE() function to the columns which are not in the GROUP BY clause (id and lastName in this example):

mysql> SELECT ANY_VALUE(id) as id, firstName, ANY_VALUE(lastName) as lastName FROM table_name GROUP BY firstName;
+----+-----------+----------+
| id | firstName | lastName |
+----+-----------+----------+
|  1 | John      | Doe      |
|  2 | Bugs      | Bunny    |
+----+-----------+----------+
2 rows in set (0.01 sec)

As written in the aforementioned docs,

In this case, MySQL ignores the nondeterminism of address values within each name group and accepts the query. This may be useful if you simply do not care which value of a nonaggregated column is chosen for each group. ANY_VALUE() is not an aggregate function, unlike functions such as SUM() or COUNT(). It simply acts to suppress the test for nondeterminism.

The Answer 9

0 people think this answer is useful

Keep in mind when using the group by and order by that MySQL is the ONLY database that allows for columns to be used in the group by and/or order by piece that are not part of the select statement.

So for example: select column1 from table group by column2 order by column3

That will not fly in other databases like Postgres, Oracle, MSSQL, etc. You would have to do the following in those databases

select column1, column2, column3 from table group by column2 order by column3

Just some info in case you ever migrate your current code to another database or start working in another database and try to reuse code.

The Answer 10

-2 people think this answer is useful

You can use group by for display distinct values and also corresponding fields.

select * from tabel_name group by FirstName

Now you got output like this:

ID    FirstName     LastName
2     Bugs          Bunny
1     John          Doe


If you want to answer like

ID    FirstName     LastName
1     John          Doe
2     Bugs          Bunny

then use this query,

select * from table_name group by FirstName order by ID

The Answer 11

-3 people think this answer is useful
SELECT DISTINCT(firstName), ID, LastName from tableName GROUP BY firstName

Would be the best bet IMO

The Answer 12

-4 people think this answer is useful
SELECT DISTINCT (column1), column2
FROM table1
GROUP BY column1

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