Pivot and unpivot for T-SQL

This topic provides reference information about feature compatibility between Microsoft SQL Server 2019 and Amazon Aurora PostgreSQL, specifically regarding the PIVOT and UNPIVOT operators. You can understand the differences in functionality and learn how to adapt your SQL queries when migrating from SQL Server to Aurora PostgreSQL.

Feature compatibility	AWS SCT / AWS DMS automation level	AWS SCT action code index	Key differences
		PIVOT and UNPIVOT	Straightforward rewrite to use traditional SQL syntax.

SQL Server Usage

PIVOT and UNPIVOT are relational operations used to transform a set by rotating rows into columns and columns into rows.

PIVOT

The PIVOT operator consists of several clauses and implied expressions.

The anchor column isn’t pivoted and results in a single row for each unique value, similar to GROUP BY.

The pivoted columns are derived from the PIVOT clause and are the row values transformed into columns. The values for these columns are derived from the source column defined in the PIVOT clause.

PIVOT Syntax

SELECT <Anchor column>,
  [Pivoted Column 1] AS <Alias>,
  [Pivoted column 2] AS <Alias>
  ...n
FROM
  (<SELECT Statement of Set to be Pivoted>)
  AS <Set Alias>
PIVOT
(
  <Aggregate Function>(<Aggregated Column>)
FOR
[<Column With the Values for the Pivoted Columns Names>]
  IN ( [Pivoted Column 1], [Pivoted column 2] ...)
) AS <Pivot Table Alias>;

PIVOT Examples

The following example creates and populates the Orders table.

CREATE TABLE Orders
(
  OrderID INT NOT NULL
  IDENTITY(1,1) PRIMARY KEY,
  OrderDate DATE NOT NULL,
  Customer VARCHAR(20) NOT NULL
);

INSERT INTO Orders (OrderDate, Customer)
VALUES
('20180101', 'John'),
('20180201', 'Mitch'),
('20180102', 'John'),
('20180104', 'Kevin'),
('20180104', 'Larry'),
('20180104', 'Kevin'),
('20180104', 'Kevin');

The following example creates a simple PIVOT for the number of orders for each day. Days of month from 5 to 31 are omitted for example simplicity.

SELECT 'Number of Orders for Day' AS DayOfMonth,
  [1], [2], [3], [4] /*...[31]*/
FROM (
  SELECT OrderID,
    DAY(OrderDate) AS OrderDay
  FROM Orders
  ) AS SourceSet
PIVOT
(
  COUNT(OrderID)
  FOR OrderDay IN ([1], [2], [3], [4] /*...[31]*/)
) AS PivotSet;

For the preceding example, the result looks as shown following.

DayOfMonth                1  2  3  4  /*...[31]*/
Number of Orders for Day  2  1  0  4

The result set is now oriented in rows against columns. The first column is the description of the columns to follow.

PIVOT for number of orders for each day, for each customer.

SELECT Customer,
  [1], [2], [3], [4] /*...[31]*/
FROM (
  SELECT OrderID,
    Customer,
    DAY(OrderDate) AS OrderDay
  FROM Orders
  ) AS SourceSet
PIVOT
(
  COUNT(OrderID)
  FOR OrderDay IN ([1], [2], [3], [4] /*...[31]*/)
) AS PivotSet;

Customer  1  2  3  4
John      1  1  0  0
Kevin     0  0  0  3
Larry     0  0  0  1
Mitch     1  0  0  0

UNPIVOT

UNPIVOT is similar to PIVOT in reverse, but spreads existing column values into rows.

The source set is similar to the result of the PIVOT with values pertaining to particular entities listed in columns. Because the result set has more rows than the source, aggregations aren’t required.

It is less commonly used than PIVOT because most data in relational databases have attributes in columns; not the other way around.

UNPIVOT Examples

The following example creates and populates the pivot-like EmployeeSales table. This is most likely a view or a set from an external source.

CREATE TABLE EmployeeSales
(
  SaleDate DATE NOT NULL PRIMARY KEY,
  John INT,
  Kevin INT,
  Mary INT
);

INSERT INTO EmployeeSales
VALUES
('20180101', 150, 0, 300),
('20180102', 0, 0, 0),
('20180103', 250, 50, 0),
('20180104', 500, 400, 100);

The following example unpivots employee sales for each date into individual rows for each employee.

SELECT SaleDate,
  Employee,
  SaleAmount
FROM
(
  SELECT SaleDate, John, Kevin, Mary
  FROM EmployeeSales
) AS SourceSet
UNPIVOT (
  SaleAmount
  FOR Employee IN (John, Kevin, Mary)
  )AS UnpivotSet;

For the preceding example, the result looks as shown following.

SaleDate    Employee  SaleAmount
2018-01-01  John      150
2018-01-01  Kevin     0
2018-01-01  Mary      300
2018-01-02  John      0
2018-01-02  Kevin     0
2018-01-02  Mary      0
2018-01-03  John      250
2018-01-03  Kevin     50
2018-01-03  Mary      0
2018-01-04  John      500
2018-01-04  Kevin     400
2018-01-04  Mary      100

For more information, see FROM - Using PIVOT and UNPIVOT in the SQL Server documentation.

PostgreSQL Usage

Amazon Aurora PostgreSQL-Compatible Edition (Aurora PostgreSQL) doesn’t support the PIVOT and UNPIVOT relational operators.

You can rewrite the functionality of these operators to use standard SQL syntax, as shown in the following examples.

PIVOT Examples

The following example creates and populates the Orders table.

CREATE TABLE Orders
(
  OrderID SERIAL PRIMARY KEY,
  OrderDate DATE NOT NULL,
  Customer VARCHAR(20) NOT NULL
);

INSERT INTO Orders (OrderDate, Customer)
VALUES
('20180101', 'John'),
('20180201', 'Mitch'),
('20180102', 'John'),
('20180104', 'Kevin'),
('20180104', 'Larry'),
('20180104', 'Kevin'),
('20180104', 'Kevin');

The following example creates a simple PIVOT for the number of orders for each day. Days of month from 5 to 31 are omitted for example simplicity.

SELECT 'Number of Orders for Day' AS DayOfMonth,
COUNT(CASE WHEN date_part('day', OrderDate) = 1 THEN 'OrderDate' ELSE NULL END) AS "1",
COUNT(CASE WHEN date_part('day', OrderDate) = 2 THEN 'OrderDate' ELSE NULL END) AS "2",
COUNT(CASE WHEN date_part('day', OrderDate) = 3 THEN 'OrderDate' ELSE NULL END) AS "3",
COUNT(CASE WHEN date_part('day', OrderDate) = 4 THEN 'OrderDate' ELSE NULL END) AS "4" /*...[31]*/
FROM Orders AS O;

For the preceding example, the result looks as shown following.

DayOfMonth                1  2  3  4  /*...[31]*/
Number of Orders for Day  2  1  0  4

PIVOT for number of orders for each day, for each customer.

SELECT Customer,
COUNT(CASE WHEN date_part('day', OrderDate) = 1 THEN 'OrderDate' ELSE NULL END) AS "1",
COUNT(CASE WHEN date_part('day', OrderDate) = 2 THEN 'OrderDate' ELSE NULL END) AS "2",
COUNT(CASE WHEN date_part('day', OrderDate) = 3 THEN 'OrderDate' ELSE NULL END) AS "3",
COUNT(CASE WHEN date_part('day', OrderDate) = 4 THEN 'OrderDate' ELSE NULL END) AS "4" /*...[31]*/
FROM Orders AS O
GROUP BY Customer;

For the preceding example, the result looks as shown following.

Customer  1  2  3  4
John      1  1  0  0
Kevin     0  0  0  3
Larry     0  0  0  1
Mitch     1  0  0  0

UNPIVOT Examples

The following example creates and populates the pivot-like EmployeeSales table. In real life this will most likely be a view, or a set from an external source.

CREATE TABLE EmployeeSales
(
  SaleDate DATE NOT NULL PRIMARY KEY,
  John INT,
  Kevin INT,
  Mary INT
);

INSERT INTO EmployeeSales
VALUES
('20180101', 150, 0, 300),
('20180102', 0, 0, 0),
('20180103', 250, 50, 0),
('20180104', 500, 400, 100);

The following example unpivots employee sales for each date into individual rows for each employee.

SELECT SaleDate, Employee, SaleAmount
FROM (
  SELECT SaleDate,
    Employee,
    CASE
      WHEN Employee = 'John' THEN 'John'
      WHEN Employee = 'Kevin' THEN 'Kevin'
      WHEN Employee = 'Mary' THEN 'Mary'
    END AS SaleAmount
  FROM EmployeeSales as emp
  CROSS JOIN
  (
    SELECT 'John' AS Employee
    UNION ALL
    SELECT 'Kevin'
    UNION ALL
    SELECT 'Mary'
  ) AS Employees
) AS UnpivotedSet;

For the preceding example, the result looks as shown following.

SaleDate    Employee  SaleAmount
2018-01-01  John      150
2018-01-01  Kevin     0
2018-01-01  Mary      300
2018-01-02  John      0
2018-01-02  Kevin     0
2018-01-02  Mary      0
2018-01-03  John      250
2018-01-03  Kevin     50
2018-01-03  Mary      0
2018-01-04  John      500
2018-01-04  Kevin     400
2018-01-04  Mary      100