Sql-server – Use a calculated column in a where clause

calculated-columnssql servertsqlwhere-clause

I'm trying to use a calculated column in a where clause.

I've trying everything from CROSS APPLY, to sub-query select but it does not give me the anything near what I need.

My query so far:

SELECT p.Code, c.AccountNumber, Sales = (SUM(p.UnitPrice) * SUM(od.QtyShipped)) FROM [dbo].Customer c 
    LEFT JOIN [dbo].OrderHeader oh ON oh.CustomerId = c.Id 
    LEFT JOIN [dbo].OrderDetail od ON od.OrderHeaderId = oh.Id
    LEFT JOIN [dbo].Product p ON p.Id = od.ProductId
WHERE Sales > 100
GROUP BY p.Code, c.AccountNumber, Sales

This does not work, as 'Sales' is an invalid column

Best Answer

You'll need to wrap the inner query in a derived table or CTE in order to be able to use derived columns in the WHERE clause (Also, note SUM() is specified just once, using the results of the multiplication):

SELECT x.Code, x.AccountNumber, x.Sales
FROM
(
  SELECT p.Code, c.AccountNumber, SUM(p.UnitPrice *od.QtyShipped) AS Sales 
  FROM [dbo].Customer c 
      LEFT JOIN [dbo].OrderHeader oh ON oh.CustomerId = c.Id 
      LEFT JOIN [dbo].OrderDetail od ON od.OrderHeaderId = oh.Id
      LEFT JOIN [dbo].Product p ON p.Id = od.ProductId
  GROUP BY p.Code, c.AccountNumber
) AS x
WHERE x.Sales > 100;

Syntax:

ALTER TABLE {TABLENAME} 
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL} 
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES

Example:

ALTER TABLE SomeTable
        ADD SomeCol Bit NULL --Or NOT NULL.
 CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
    DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.

Notes:

Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6

Optional With-Values Statement:
The WITH VALUES is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES or not.

How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable and do not Specify SomeCol's value, then it will Default to 0.
If you insert a Record and Specify SomeCol's value as NULL (and your column allows nulls),
then the Default-Constraint will not be used and NULL will be inserted as the Value.

Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.

Sql-server – How to check if a column exists in a SQL Server table

SQL Server 2005 onwards:

IF EXISTS(SELECT 1 FROM sys.columns 
          WHERE Name = N'columnName'
          AND Object_ID = Object_ID(N'schemaName.tableName'))
BEGIN
    -- Column Exists
END

Martin Smith's version is shorter:

IF COL_LENGTH('schemaName.tableName', 'columnName') IS NOT NULL
BEGIN
    -- Column Exists
END

Best Answer

Related Solutions

Sql – Add a column with a default value to an existing table in SQL Server

Syntax:

Example:

Notes:

Sql-server – How to check if a column exists in a SQL Server table

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