CODEWITHSUNDEEP
sqldatabasestringnullconcatenation
LuckySlevin
LuckySlevin

Reputation: 745

Concatenate with NULL values in SQL

Column1      Column2
-------      -------
 apple        juice
 water        melon
 banana
 red          berry

I have a table which has two columns. Column1 has a group of words and Column2 also has a group of words. I want to concatenate them with + operator without a space.

For instance: applejuice

The thing is, if there is a null value in the second column, I only want to have the first element as a result.

For instance: banana

Result
------
applejuice
watermelon
banana
redberry

However, when I use column1 + column2, it gives a NULL value if Column2 is NULL. I want to have "banana" as the result.

Upvotes: 38

Views: 129282

Answers (9)

Chris
Chris

Reputation: 3162

The + sign for concatenation in TSQL will by default combine string + null to null as an unknown value.

You can do one of two things, you can change this variable for the session which controls what Sql should do with Nulls

http://msdn.microsoft.com/en-us/library/ms176056.aspx

Or you can Coalesce each column to an empty string before concatenating.

COALESCE(Column1, '')

http://msdn.microsoft.com/en-us/library/ms190349.aspx

Upvotes: 0

CapelliC
CapelliC

Reputation: 60014

If you are using MySql, use ifnull(Column2, '')

Upvotes: 1

WebChemist
WebChemist

Reputation: 4411

I know this is old, but since no one mentioned it - if using MySQL, you can just use the CONCAT_WS() function, which will skip null values when combining column values.

You can test this by running this query:

SELECT CONCAT_WS('', col1, col2) AS title
FROM
(
    SELECT   'apple' AS col1
            ,'juice' AS col2
    UNION
    SELECT   'water'        
            ,'melon'
    UNION
    SELECT   'banana'   
            ,NULL
    UNION
    SELECT   'red'
            ,'berry'
) a

Which gives the desired example result:

applejuice
watermelon
banana
redberry

Upvotes: 0

Client Relations
Client Relations

Reputation: 137

A few posts I have made tagged MSSQL have been renamed to 'SQL' by a moderator. So I am assuming you are using MSSQL

COALESCE will return the FIRST non-null value.

SELECT COALESCE('a', NULL, 'c')

will only return 'a'

If you want Firstname + Lastname, where sometimes one or the other is NULL, use CONCAT. Concat adds the strings together and replaces NULLS with 0 length non-null value.

 SELECT CONCAT('a', NULL, 'c')

will return 'ac'

If you want Fn space + middle name space + LN, combine concatinate with CONCAT:

SELECT CONCAT('a' + ' ', NULL + ' ', 'c')

Will return 'a c'.

The space after middlename (null) is eliminated with the + and NULL.

NULL + ' ' is null.

So in cases where Middlename or Firstname is null, you won't get extra unwanted spaces.

Upvotes: 7

harsh
harsh

Reputation: 11

You can use a case condition: 

case when column_2 is not null 
     then concatenate
     else column_1
end

Upvotes: 0

Chris Cooper
Chris Cooper

Reputation: 17564

You can do a union:

(SELECT Column1 + Column2 FROM Table1 WHERE Column2 is not NULL)
UNION
(SELECT Column1 FROM Table1 WHERE Column2 is NULL);

Upvotes: 0

Jonathan Leffler
Jonathan Leffler

Reputation: 753930

Standard SQL requires that string concatenation involving a NULL generates a NULL output, but that is written using the || operation:

SELECT a || b
  FROM SomeTable;

The output will be null if either a or b or both contains a NULL.

Using + to concatenate strings indicates that you are using a DBMS-specific extension. The behaviour might be the same as the standard requires - indeed, that seems to be the gist of your question.

Some DBMS - notably Oracle - tend to treat null strings as equivalent to empty strings; then you can concatenate away merrily. However, that behaviour is not strictly standard-compliant if the || operator is used.

Consider using COALESCE or NVL or IFNULL or some similar function to map the NULL to an empty string before concatenating.

Upvotes: 4

Chris E
Chris E

Reputation: 983

I'm not certain what you're using as your database, but I would look for a "coalesce" function for your particular SQL dialect and use that.

Upvotes: 0

Joe Stefanelli
Joe Stefanelli

Reputation: 135808

Use the COALESCE function to replace NULL values with an empty string.

SELECT Column1 + COALESCE(Column2, '') AS Result
    FROM YourTable

Upvotes: 77

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