Creative uses for COALESCE() in SQL Server

Now whenever you need this script (regardless of what the columns are actually named) just call the function and pass the three columns. In the examples below, I'm passing literals, but you can substitute column names and achieve the same results:

SELECT dbo.WholeName('James',NULL,'Bond')
UNION
SELECT dbo.WholeName('Cher',NULL,NULL)
UNION
SELECT dbo.WholeName('John','F.','Kennedy')

Here is the result set:

Cher  
James  Bond
John F. Kennedy

You'll notice a hole in our thinking -- there are two spaces in James Bond's name. It's easy to fix this by changing the @result line to the following:

SELECT @Result = LTRIM(@first + ' ' + COALESCE(@middle,'') + ' ') + COALESCE(@last,'')

Here's another use of COALESCE(). In this example, I will produce a list of monies paid to employees. The problem is there are different payment arrangements for different employees (e.g., some employees are paid by the hour, by piece work, with a weekly salary, or by commission).

Here is the code to create a sample table:

CREATE TABLE [Coalesce_Demo].[PayDay](
      [EmployeeID] [int] NOTNULL,
      [HourlyWage] [money] NULL,
      [HoursPerWeek] [int] NULL,
      [AmountPerPiece] [money] NULL,
      [PiecesThisWeek] [int] NULL,
      [WeeklySalary] [money] NULL,
      [CommissionThisWeek] [int] NULL,
 CONSTRAINT [PK_PayDay] PRIMARYKEYCLUSTERED
(
      [EmployeeID] ASC
)WITH(PAD_INDEX  =OFF,STATISTICS_NORECOMPUTE  =OFF,IGNORE_DUP_KEY=OFF,ALLOW_ROW_LOCKS  =ON,ALLOW_PAGE_LOCKS  =ON)ON [PRIMARY]
)ON [PRIMARY]

Here are a few sample rows, one of each type:

1     18.0040    NULL  NULL  NULL  NULL
2     NULL  NULL  4.00  400   NULL  NULL
3     NULL  NULL  NULL  NULL  800.00      NULL
4     NULL  NULL  NULL  NULL  500.00      600

Use the following code to list the amount paid to employees (regardless of how they are paid) in a single column:

SELECT
      EmployeeID,
      COALESCE(HourlyWage * HoursPerWeek,0)+
      COALESCE(AmountPerPiece * PiecesThisWeek,0)+
      COALESCE(WeeklySalary + CommissionThisWeek,0)AS Payment
FROM [Coalesce_Demo].[PayDay]

Here is the result set:

EmployeeID  Payment
1     720.00
2     1600.00
3     800.00
4     1100.00

You might need that expression in several places in your application and, although it works, it isn't very graceful. This is how you can create a calculated column to do it:

ALTER TABLE Coalesce_Demo.PayDay
ADD Payment AS
      COALESCE(HourlyWage * HoursPerWeek,0)+
      COALESCE(AmountPerPiece * PiecesThisWeek,0)+
      COALESCE(WeeklySalary + CommissionThisWeek,0)

Now a simple SELECT * displays the pre-calculated results.

Summary

This tip demonstrates some unusual ways and places to apply the power of COALESCE(). In my experience, COALESCE() most often appears within a very specific content, such as in a query or view or stored procedure.

You can generalise the use of COALESCE() by placing it in a function. You can also optimise its performance and make its results constantly available by placing it in a calculated column.