SQL How to Split One Column into Multiple Variable Columns - sql

Question

I am working on MSSQL, trying to split one string column into multiple columns. The string column has numbers separated by semicolons, like:
190230943204;190234443204;
However, some rows have more numbers than others, so in the database you can have
190230943204;190234443204;
121340944534;340212343204;134530943204
I've seen some solutions for splitting one column into a specific number of columns, but not variable columns. The columns that have less data (2 series of strings separated by commas instead of 3) will have nulls in the third place.
Ideas? Let me know if I must clarify anything.

Answer 1

Splitting this data into separate columns is a very good start (coma-separated values are an heresy). However, a "variable number of properties" should typically be modeled as a one-to-many relationship.
CREATE TABLE main_entity (
id INT PRIMARY KEY,
other_fields INT
);
CREATE TABLE entity_properties (
main_entity_id INT PRIMARY KEY,
property_value INT,
FOREIGN KEY (main_entity_id) REFERENCES main_entity(id)
);
entity_properties.main_entity_id is a foreign key to main_entity.id.
Congratulations, you are on the right path, this is called normalisation. You are about to reach the First Normal Form.
Beweare, however, these properties should have a sensibly similar nature (ie. all phone numbers, or addresses, etc.). Do not to fall into the dark side (a.k.a. the Entity-Attribute-Value anti-pattern), and be tempted to throw all properties into the same table. If you can identify several types of attributes, store each type in a separate table.

Answer 2

If these are all fixed length strings (as in the question), then you can do the work fairly simply (at least relative to other solutions):
select substring(col, 1+13*(n-1), 12) as val
from t join
(select 1 as n union all select union all select 3
) n
on len(t.col) <= 13*n.n
This is a useful hack if all the entries are the same size (not so easy if they are of different sizes). Do, however, think about the data structure because semi-colon (or comma) separated list is not a very good data structure.

Answer 3

IF I were you, I would create a simple function that is dividing values separated with ';' like this:
IF EXISTS (SELECT * FROM sysobjects WHERE id = object_id(N'fn_Split_List') AND xtype IN (N'FN', N'IF', N'TF'))
BEGIN
DROP FUNCTION [dbo].[fn_Split_List]
END
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE FUNCTION [dbo].[fn_Split_List](#List NVARCHAR(512))
RETURNS #ResultRowset TABLE ( [Value] NVARCHAR(128) PRIMARY KEY)
AS
BEGIN
DECLARE #XML xml = N'<r><![CDATA[' + REPLACE(#List, ';', ']]></r><r><![CDATA[') + ']]></r>'
INSERT INTO #ResultRowset ([Value])
SELECT DISTINCT RTRIM(LTRIM(Tbl.Col.value('.', 'NVARCHAR(128)')))
FROM #xml.nodes('//r') Tbl(Col)
RETURN
END
GO
Than simply called in this way:
SET NOCOUNT ON
GO
DECLARE #RawData TABLE( [Value] NVARCHAR(256))
INSERT INTO #RawData ([Value] )
VALUES ('1111111;22222222')
,('3333333;113113131')
,('776767676')
,('89332131;313131312;54545353')
SELECT SL.[Value]
FROM #RawData AS RD
CROSS APPLY [fn_Split_List] ([Value]) as SL
SET NOCOUNT OFF
GO
The result is as the follow:
Value
1111111
22222222
113113131
3333333
776767676
313131312
54545353
89332131
Anyway, the logic in the function is not complicated, so you can easily put it anywhere you need.
Note: There is not limitations of how many values you will have separated with ';', but there are length limitation in the function that you can set to NVARCHAR(MAX) if you need.
EDIT:
As I can see, there are some rows in your example that will caused the function to return empty strings. For example:
number;number;
will return:
number
number
'' (empty string)
To clear them, just add the following where clause to the statement above like this:
SELECT SL.[Value]
FROM #RawData AS RD
CROSS APPLY [fn_Split_List] ([Value]) as SL
WHERE LEN(SL.[Value]) > 0