SQL Server update statement performance - sql

Question

I have problem in optimizing an SQL query to do some data cleansing.
In fact, I have a table which is a sort of referential of a multiple special characters and word. Let's call it ABNORMAL(ID,PATTERN)
I have also another table INDIVIDUALS containing a column (NAME) which I want to clean by removing from it all characters that exist in the table ABNORMAL.
Currently, I have tried to use update statements, but I'm not sure if there is a better way to do this.
Approach one
Use a while loop to build a replace containing all characters from ABNORMALS by a blank '' and do one update using the built-in REPLACE
DECLARE #REPLACE_EXPRESSION nvarchar(max) ='REPLACE(NAME,'''','''')'
DECLARE #i int = 1
DECLARE #nbr int = (SELECT COUNT(*) FROM ABNORMAL)
-- CURRENT_CHARAC
DECLARE #CURRENT_CHARAC nvarchar(max)
-- NEW REPLACE EXPRESSION TO IMBRICATE INTO THE REPLACE EXPRESSION VARIABLE
DECLARE #CURR_REP NVARCHAR(max)
-- STRING TO BUILD AN SQL QUERY CONTAINING THE REPLACE EXPRESSION
DECLARE #UPDATE_QUERY nvarchar(max)
WHILE #i < #nbr
BEGIN
SELECT #CURRENT_CHARAC=PATTERN FROM CLEANSING_STG_PRISM_FRA_REF_UNSIGNIFICANT_VALUES WHERE ID_PATTERN=#i ;
SET #REPLACE_EXPRESSION = REPLACE(#REPLACE_EXPRESSION ,'NAME','REPLACE(NAME,'+''''+#CURRENT_CHARAC+''''+','''')')
set #i=#i+1
END
SET #UPDATE_QUERY = 'UPDATE INDIVIDUAL SET NAME ='+ #REPLACE_EXPRESSION
EXEC sp_executesql #UPDATE_QUERY
Approach two
Use a while loop to select every character in abnormal and do an update using replace containing the characters to remove:
DECLARE #i int = 1
DECLARE #nbr int = (SELECT COUNT(*) FROM ABNORMAL)
-- CURRENT_CHARAC
DECLARE #CURRENT_CHARAC nvarchar(max)
-- STRING TO BUILD AN SQL QUERY CONTAINING THE REPLACE EXPRESSION
DECLARE #UPDATE_QUERY nvarchar(max)
WHILE #i < #nbr
BEGIN
SELECT #CURRENT_CHARAC=PATTERN FROM CLEANSING_STG_PRISM_FRA_REF_UNSIGNIFICANT_VALUES WHERE ID_PATTERN=#i ;
UPDATE INDIVIDUAL
SET NAME = REPLACE(NAME,#CURRENT_CHARAC,'')
SET #i=#i+1
END
I already tested both approaches for 2 millions records, and I found that the first approach is faster than the second. I would know if you have already done something similar and new (better) ideas to try.

Answer 1

If you are using SQL Server 2017 you could use TRANSLATE and avoid dynamic SQL:
SELECT i.*
, REPLACE(TRANSLATE(i.NAME, f, REPLICATE('!', s.l)), '!', '') AS cleansed
FROM INDIVIDUALS i
OUTER APPLY (SELECT STRING_AGG(PATTERN, '') AS f
,LEN(STRING_AGG(PATTERN,'')) AS l
FROM ABNORMAL) AS s
DBFiddle Demo
Anyway 1st approach is better becasue you do one UPDATE, with second approach you remove characters one character at time (so you will have multiple UPDATE).
I would also track transaction log growth with both approaches.

Answer 2

If there's not too many characters that to be cleaned, then this trick might work.
Basically, you build 1 big update statement with a replace for each value in the table with the characters to be removed.
Example code:
Test data (using temp tables)
create table #ABNORMAL_CHARACTERS (id int identity(1,1), chr varchar(30));
insert into #ABNORMAL_CHARACTERS (chr) values ('!'),('&'),('#');
create table #INDIVIDUAL (id int identity(1,1), name varchar(30));
insert into #INDIVIDUAL (name) values ('test 1 &'),('test !&#2'),('test 3');
Code:
declare #FieldName varchar(30) = 'name';
declare #Replaces varchar(max) = #FieldName;
declare #UpdateSQL varchar(max);
select #Replaces = concat('replace('+#Replaces+', ', ''''+chr+''','''')') from #ABNORMAL_CHARACTERS order by id;
set #UpdateSQL = 'update #INDIVIDUAL
set name = '+#Replaces + '
where exists (select 1 from #ABNORMAL_CHARACTERS where charindex(chr,name)>0)';
exec (#UpdateSQL);
select * from #INDIVIDUAL;
A test here on rextester
And if you would have a UDF that can do a regex replace.
For example here
Then the #Replaces variable could be simplified with only 1 RegexReplace function and a pattern.