33
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 Comunm2 is NULL. I want to have "banana" as the result.

dreftymac
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LuckySlevin
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    This is the case with more than just strings I've found. I dont know if its the most efficient but you could always wrap the columns in an isNull statement. ie: isNull(column1, '') + isNull(column2,'') what that should do is when it finds null it will replace it with an empty string. I haven't tested this so let me know if it works. – Chris Santiago Nov 22 '11 at 21:03
  • Possible duplicate of [SQL Server String Concatenation with Null](http://stackoverflow.com/questions/2916791/sql-server-string-concatenation-with-null) – Michael Freidgeim Mar 09 '16 at 22:15

8 Answers8

64

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

SELECT Column1 + COALESCE(Column2, '') AS Result
    FROM YourTable
Joe Stefanelli
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6

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.

Client Relations
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  • This is perfect! I had to do an RTRIM(LTRIM(x)) on the fields, and then I did a case statement to check if the last character of the concatenation was the delimiter I was using (;) so I could strip that off, in case there was an extra one at the end. – missscripty Nov 10 '20 at 16:39
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    @Client Relations You are not correct actually because SELECT CONCAT('a' + ' ', NULL + ' ', 'c') will return Null not 'ac' – Pranjal sharma Jan 05 '23 at 14:02
4

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.

Jonathan Leffler
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1

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

CapelliC
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0

You can use a case condition: 

case when column_2 is not null 
     then concatenate
     else column_1
end
trincot
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harsh
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  • this doesn't add anything useful to the other 6 existing answers – Adam Apr 13 '17 at 22:21
  • @Adam, actually no-one had yet suggested the `case` expression as solution. I think your assessment is maybe too harsh. – trincot Apr 13 '17 at 23:50
0

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.

Chris E
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0

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 controlls 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

Chris
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0

You can do a union:

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