Select a column if other column is null

I need to select a field called ProgramID from a table and if the ProgramID is NULL then I need to select the value in the InterimProgramID from the same table and alias it as ProgramID.

How can I make a conditional SELECT statement to do this?

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最佳答案

You need the ISNULL function.

SELECT ISNULL(a, b)

b gets selected if a is null.

Also, you can use the WHEN/THEN select option, lookup in BOL. Essentially: its c switch/case block meets SQL.

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You can use either the ISNULL function or the COALESCE function. They both do pretty much the same thing, however ISNULL only takes two parameters and COALESCE takes multiple parameters (returning the first non-null it encounters). Both try the first param, then the second, (and COALESCE continues on)

DECLARE @IAMNULL VARCHAR
DECLARE @IAMNOTNULL VARCHAR
SET @IAMNOTNULL = 'NOT NULL'


SELECT ISNULL(@IAMNULL, @IAMNOTNULL)
--Output: 'NOT NULL'


DECLARE @IAMNULLALSO VARCHAR


SELECT COALESCE(@IAMNULL, @IAMNULLALSO, @IAMNOTNULL)
--Output: 'NOT NULL'
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  select COALESCE ( ProgramID , InterimProgramID ) as 'ProgramID'
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SELECT ProgramID
FROM a_table
WHERE ProgramID IS NOT NULL
UNION
SELECT InterimProgramID AS ProgramID
FROM a_table
WHERE ProgramID IS NULL;
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You can also use IFNULL function

select IFNULL(ProgramId,interimId) as ProgramId
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Coalesce('zzz-' + ProgramID, InterimID) as programID will still ignore ProgramID even if you have a pretext value. It's a cool little function

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There is also:

Select NVL(Column_A, Column_B) From 'schema'.'table_name'

The NVL( ) function is available in Oracle, and not in MySQL or SQL Server. This function is used to replace NULL value with another value. It is similar to the IFNULL Function in MySQL and the ISNULL Function in SQL Server.

https://www.1keydata.com/sql/sql-nvl.html


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