Replacing Null and Empty String Within Select Statement

Replacing NULL and empty string within Select statement

Try this

COALESCE(NULLIF(Address.COUNTRY,''), 'United States')

MySql Query Replace NULL with Empty String in Select

Some of these built-in functions should work:

COALESCE(value,...)

Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.

IS NULL

Tests whether a value is NULL.

IFNULL(expr1,expr2)

If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2.

How to replace NULL with empty string in SQL?

Try IsNull

select ISNULL(Column,'') as ColumnName

OR COALESCE

select COALESCE(NULLIF(ColumnName,''), 'Column')

How to replace null field values with an empty string?

The problem occurs when the subquery returns no values. The isnull() needs to go outside the subquery:

ISNULL( (SELECT TOP 1 a2.AAAREFNUMVALUE
         FROM dbo.AAATOREFNUMS a2
         WHERE a2.AAATRANSPORTTABLE  = a.AAATRANSPORTTABLE  AND 
               a2.AAAREFNUMTYPE = 4 
         ORDER BY a2.AAAREFNUMVALUE
        ), ''
      ) AS "Estimate Number"

Note that this is a situation where ISNULL() is preferred over COALESCE(), because the SQL Server implementation of COALESCE() evaluates the first argument twice when it is not NULL.

However, you might find the query easier to express and faster to run if you use window functions instead:

SELECT DISTINCT a.AAAREFNUMVALUE AS "Pro Number",
       COALESCE(a.AAAREFNUMVALUE_4, '') as "Estimate Number"
FROM (SELECT a.*,
             MAX(CASE WHEN a.AAAREFNUMTYPE = 4 THEN a.AAAREFNUMVALUE END) OVER (PARTITION BY a.AAATRANSPORTTABLE) as AAAREFNUMVALUE_4
      FROM dbo.AAATOREFNUMS a
     ) a INNER JOIN
     dbo.AAATODATES d
     ON a.AAATRANSPORTTABLE = d.AAATRANSPORTTABLE
WHERE a.AAAREFNUMTYPE = 1 AND d.AAADATETYPE = 1  ;

SQL Server replacing null with empty string

You can't check a column value for NULL using the = operator, because the result will also be NULL. Instead, you should use IS NULL and IS NOT NULL. But for readability purposes, I would use COALESCE instead of CASE statements.

Use COALESCE:

SELECT CONCAT(COALESCE(Episode_Name, ' '),
              '-',
              COALESCE(Pnr_FName, ' '),
              COALESCE(Pnr_LName, ' '),
              COALESCE(Guest, ' '),
              '-',
              COALESCE(Car_Make, ' '))
FROM EPISODES, PRESENTERS, CARS

By the way, you should use explicit join syntax instead of using commas in the FROM clause, e.g.

FROM EPISODES e INNER JOIN PRESENTERS p
    ON e.col = p.col

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