How to Unpivot Table in MySQL

Last updated on May 17th, 2020 at 06:25 am

Sometimes you need to transpose columns into rows, or unpivot table in MySQL. Since MySQL doesn’t have a function to UNPIVOT or REVERSE PIVOT a table, you need to write a SQL query to transpose columns into rows. Here’s how to unpivot table in MySQL.

Table of Contents

How to Unpivot Table in MySQL

Let’s say you have the following pivot table

mysql>create table data(id int, a varchar(255), b varchar(255), c varchar(255));
mysql>insert into data(id,a,b,c) values(1,'a1','b1','c1'),(2,'a1','b1','c1');
mysql>select * from data;

+------+------+------+------+
| id   | a    | b    | c    |
+------+------+------+------+
|    1 | a1   | b1   | c1   |
|    2 | a1   | b1   | c1   |
+------+------+------+------+

Let’s say you want to unpivot table in MySQL to the following.

1 | a1 | a
1 | b1 | b
1 | c1 | c
2 | a2 | a
2 | b2 | b
2 | c2 | c

Bonus Read : How to Create Dynamic Pivot Tables in MySQL

Unpivot Table in MySQL

Here’s the query to do unpivot in SQL. Since MySQL doesn’t offer an UNPIVOT function, You need to use UNION ALL clause in to reverse pivot a table in MySQL.

mysql> select id, 'a' col, a value
      from data
      union all
      select id, 'b' col, b value
      from data
      union all
      select id, 'c' col, c value
      from data;
+------+-----+-------+
| id   | col | value |
+------+-----+-------+
|    1 | a   | a1    |
|    2 | a   | a1    |
|    1 | b   | b1    |
|    2 | b   | b1    |
|    1 | c   | c1    |
|    2 | c   | c1    |
+------+-----+-------+

In the above query, we basically cut the original table into 3 smaller ones – one for each column a,b,c and then append them one below the other using UNION ALL.

If you want to filter rows, you can add a WHERE clause as shown below

mysql> select id, 'a' col, a value
      from data
      WHERE condition
      union all
      select id, 'b' col, b value
      from data
      WHERE condition
      union all
      select id, 'c' col, c value
      from data
      WHERE condition;

Bonus read: How to Transpose Rows to Columns Dynamically in MySQL

Unfortunately, it is tedious but one of the only 2 ways to unpivot in MySQL. The other one involves doing a cross join, as shown below.

mysql> select t.id,
       c.col,
       case c.col
         when 'a' then a
         when 'b' then b
         when 'c' then c
       end as data
     from data t
     cross join
     (
       select 'a' as col
       union all select 'b'
       union all select 'c'
     ) c;
+------+-----+------+
| id   | col | data |
+------+-----+------+
|    1 | a   | a1   |
|    2 | a   | a1   |
|    1 | b   | b1   |
|    2 | b   | b1   |
|    1 | c   | c1   |
|    2 | c   | c1   |
+------+-----+------+

Bonus Read : How to Automate Pivot Table Queries in MySQL

You can customize the above query to unpivot table in MySQL, using WHERE clause. You can also use a reporting tool to plot the result in a table. Here’s an example of a table created using Ubiq.