how to deleting part of an entry - sql

Question

say if I have a column containing
hello;world;how;are;you;
how do I write a sql command to just delete "hello world" or "how are you".
thanks

Answer 1

trojanfoe wrote what you need to do with a correct database design. If you can't change this I may have a possible way todo it.
I doubt it is the fastest way to do so, but you can fetch the data, split it into a new virtual table and then remove what you need, the result you can add again in your column.
There is no split in SQL, so here is a split function (MS SQL, maybe need to modify for mySQL):
CREATE FUNCTION dbo.fn_Split(#text nvarchar(4000), #delimiter char(1) = ',')
RETURNS #Strings TABLE (
position int IDENTITY PRIMARY KEY,
value nvarchar(4000)
)
AS
BEGIN
DECLARE #index int
SET #index = -1
SET #text = RTRIM(LTRIM(#text))
WHILE (LEN(#text) > 0)
BEGIN
SET #index = CHARINDEX(#delimiter , #text)
IF (#index = 0) AND (LEN(#text) > 0)
BEGIN
INSERT INTO #Strings VALUES (#text)
BREAK
END
IF (#index > 1)
BEGIN
INSERT INTO #Strings VALUES (LEFT(#text, #index - 1))
SET #text = RIGHT(#text, (LEN(#text) - #index))
END
ELSE
SET #text = RIGHT(#text, (LEN(#text) - #index))
END
RETURN
END
With this you can do stuff like this:
SELECT * FROM dbo.fn_Split(<yourcolumn>,';')
Which gives you then your content as single rows.
Then you can remove items by using a WHERE statement like
SELECT * FROM dbo.fn_Split(<yourcolumn>,';') WHERE [value] LIKE '%hello%'
You might need to write a PROCEDURE then or a TABLE/SCALAR FUNCTION to handle you data with this.
So isn't a good way to do but the only way I found out so far :) Hope it helps a but.

Answer 2

If this column contains multiple items that you want to manipulate then putting them into a single column is a schema design flaw.
You are not taking advantage of the relational nature of the database and you should store these items in a child table of the main table. You will then be able to define ordering in this child table (with a separate column) and will be able to manipulate (i.e. SELECT, DELETE, etc) individual elements far easier.

Answer 3

Guess if it's a legacy database structure it cannot be changed easily.
Btw the answer is updating the field. Since almost every database engine nowadays allows you to write a stored function, I guess that's a good solution.
Using Oracle's Syntax something like this would work:
UPDATE TABLE SET FIELD_NAME = STORED_FUNCTION_MANIPULATING_THE_FIELD(FIELD_NAME) WHERE [where condition]
but before executing the query, you should define the stored function.
FUNCTION STORED_FUNCTION_MANIPULATING_THE_FIELD(FIELD_NAME VARCHAR2) RETURN VARCHAR2 IS
BEGIN
-- Do whatever you want on field, then return it.
END STORED_FUNCTION_MANIPULATING_THE_FIELD;
However this is conceptually wrong, multiple data values, shall use multiple columns in order to take fully advantage of relational engines (as stated in previous answers).
Regards
M.

Answer 4

UPDATE tablename SET field=replace(replace(field,'hello;world;',''),';',' ') [WHERE condition]
UPDATE tablename SET field=replace(mid(field,locate('how',field)),';',' ') [WHERE condition]
UPDATE tablename SET field=replace(mid(field,1,locate(';how',field)),';',' ') [WHERE condition]
UPDATE tablename SET field=replace(substring_index(field,';',2),';',' ') [WHERE condition]
(If you use a -2 in the substring_index function, you get the other part of the text.)
One of those will give you what you want. The use of substring_index is probably the most flexible way.