Sql Multiple Replace based on query - sql

Question

I have been trying to set up a SQL function to build descriptions with "tags". For example, I would want to start with a description:
"This is [length] ft. long and [height] ft. high"
And modify the description with data from a related table, to end up with:
"This is 75 ft. long and 20 ft. high"
I could do this easily with REPLACE functions if we had a set number of tags, but I want these tags to be user defined, and each description may or may not have specific tags in it. Would there be any better way to get this other than using a cursor to go through the string once for each available tag? Does SQL have any built in functionality to do a multiple replace? something like:
Replace(description,(select tag, replacement from tags))

Answer 1

I actually recommend doing this in application code. But, you can do it using a recursive CTE:
with t as (
select t.*, row_number() over (order by t.tag) as seqnum
from tags t
),
cte as (
select replace(#description, t.tag, t.replacement) as d, t.seqnum
from t
where seqnum = 1
union all
select replace(d, t.tag, t.replacement), t.seqnum
from cte join
t
on t.seqnum = cte.seqnum + 1
)
select top 1 cte.*
from cte
order by seqnum desc;

Answer 2

Try below query :
SELECT REPLACE(DESCRIPTION,'[length]',( SELECT replacement FROM tags WHERE tag
= '[length]') )

Answer 3

I agree with Gordon that this is best handled in your application code.
If for whatever reason that option is not available however, and if you don't want to use recursion as per Gordon's answer, you could use a tally table approach to swap out your values.
You will need to test the performance of the for xml being executed for each value though...
Assuming you have a table of Tag replacement values:
create table TagReplacementTable(Tag nvarchar(50), Replacement nvarchar(50));
insert into TagReplacementTable values('[test]',999)
,('[length]',75)
,('[height]',20)
,('[other length]',40)
,('[other height]',50);
You can create an inline table function that will work through your Descriptions and drop replace the necessary parts using TagReplacementTable as reference:
create function dbo.Tag_Replace(#str nvarchar(4000)
,#tagstart nvarchar(1)
,#tagend nvarchar(1)
)
returns table
as
return
(
with n(n) as (select n from (values(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n(n))
-- Select the same number of rows as characters in #str as incremental row numbers.
-- Cross joins increase exponentially to a max possible 10,000 rows to cover largest #str length.
,t(t) as (select top (select len(#str) a) row_number() over (order by (select null)) from n n1,n n2,n n3,n n4)
-- Return the position of every value that starts or ends a part of the description.
-- This will be the first character (t='f'), the start of any tag (t='s') and the end of any tag (t='e').
,s(s,t) as (select 1, 'f'
union all select t+1, 's' from t where substring(#str,t,1) = #tagstart
union all select t+1, 'e' from t where substring(#str,t,1) = #tagend
)
-- Return the start and length of every value, to use in the SUBSTRING function.
-- ISNULL/NULLIF combo handles the last value where there is no delimiter at the end of the string.
-- Using the t value we can determine which CHARINDEX to look for.
,l(t,s,l) as (select t,s,isnull(nullif(charindex(case t when 'f' then #tagstart when 's' then #tagend when 'e' then #tagstart end,#str,s),0)-s,4000) from s)
-- Each element of the string is returned in an ordered list along with its t value.
-- Where this t value is 's' this means the value is a tag, so append the start and end identifiers and join to the TagReplacementTable.
-- Where no replacement is found, simply return the part of the Description.
-- Finally, concatenate into one string value.
select (select isnull(r.Replacement,k.Item)
from(select row_number() over(order by s) as ItemNumber
,case when l.t = 's' then '[' else '' end
+ substring(#str,s,l)
+ case when l.t = 's' then ']' else '' end as Item
,t
from l
) k
left join TagReplacementTable r
on(k.Item = r.Tag)
order by k.ItemNumber
for xml path('')
) as NewString
);
And then outer apply to the results of the function to do replacements on all your Description values:
declare #t table (Descr nvarchar(100));
insert into #t values('This is [length] ft. long and [height] ft. high'),('[test] This is [other length] ft. long and [other height] ft. high');
select *
from #t t
outer apply dbo.Tag_Replace(t.Descr,'[',']') r;
Output:
+--------------------------------------------------------------------+-----------------------------------------+
| Descr | NewString |
+--------------------------------------------------------------------+-----------------------------------------+
| This is [length] ft. long and [height] ft. high | This is 75 ft. long and 20 ft. high |
| [test] This is [other length] ft. long and [other height] ft. high | 999 This is 40 ft. long and 50 ft. high |
+--------------------------------------------------------------------+-----------------------------------------+

Answer 4

I would not iterate through an individual string, but instead run the update on the entire column of strings. I'm not sure if that was your intent but this would be much quicker than one string at a time.
Test Data:
Create TABLE #strs ( mystr VARCHAR(MAX) )
Create TABLE #rpls (i INT IDENTITY(1,1) NOT NULL, src VARCHAR(MAX) , Trg VARCHAR(MAX) )
INSERT INTO #strs
( mystr )
SELECT 'hello ##color## world'
UNION ALL SELECT 'see jack ##verboftheday##! ##verboftheday## Jack, ##verboftheday##!'
UNION ALL SELECT 'on ##Date##, the ##color## StockMarket was ##MarketDirection##!'
INSERT INTO #rpls ( src ,Trg )
SELECT '##Color##', 'Blue'
UNION SELECT ALL '##verboftheday##' , 'run'
UNION SELECT ALL '##Date##' , CONVERT(VARCHAR(MAX), GETDATE(), 9)
UNION SELECT ALL '##MarketDirection##' , 'UP'
then a loop like this:
DECLARE #i INTEGER = 0
DECLARE #count INTEGER
SELECT #count = COUNT(*)
FROM #rpls R
WHILE #i < #count
BEGIN
SELECT #i += 1
UPDATE #strs
SET mystr = REPLACE(mystr, ( SELECT R.src
FROM #rpls R
WHERE i = #i ), ( SELECT R.Trg
FROM #rpls R
WHERE i = #i ))
END
SELECT *
FROM #strs S
Yielding the following
hello Blue world
see jack run! run Jack, run!
on May 19 2017 9:48:02:390AM, the Blue StockMarket was UP!

Answer 5

I found someone wanting to do something similar here with a set number of options:
SELECT #target = REPLACE(#target, invalidChar, '-')
FROM (VALUES ('~'),(''''),('!'),('#'),('#')) AS T(invalidChar)
I could modify it as such:
declare #target as varchar(max) = 'This is [length] ft. long and [height] ft. high'
select #target = REPLACE(#target,'[' + tag + ']',replacement)
from tags
It then runs the replace once for every record returned in the select statement.
(I originally had added this to my question, but it sounds like it is better protocol to add it as a answer.)