SQL replace 2-3 letter value in string - sql

Question

I have a table with contacts and their key skills where values are divided by a semicolon:
And I can't figure out how to replace short key skills without harming the existing longer skills. E.g. UI is included in word Building
For more than 4 letters I'm using below SQL script to replace value1 (#current) for value2 (#replace) just fine
DECLARE #current varchar(50) = 'UI'
DECLARE #replace varchar(50) = 'New Skill'
UPDATE database.dbo.contact
SET key_skill = CASE
WHEN key_skill LIKE '%'+#replace+'%'+#current THEN REPLACE(key_skill, ';'+#current, '')
WHEN key_skill LIKE '%'+#current+'%'+#replace THEN REPLACE(key_skill, #current+';', '')
WHEN (key_skill LIKE '%'+#replace+'%'+#current+'%') OR (key_skill LIKE '%'+#current+'%'+#replace+'%') THEN REPLACE(key_skill, #current+';', '')
WHEN key_skill LIKE '%'+#current+'%' THEN REPLACE(key_skill, #current, #replace)
ELSE key_skill END
FROM database.dbo.contact
WHERE (key_skill LIKE '%'+#current+'%')

Answer 1

If it is at all possible you should change your design as soon as possible. There is almost never a good reason to store lists as delimited strings in a database. Databases already have the perfect structure for storing lists, they are called tables. A second table that links contacts to skills will be really useful here. Something like this:
CREATE TABLE dbo.Contact
(
ContactID INT IDENTITY (1, 1) NOT NULL,
Name VARCHAR(255) NOT NULL,
CONSTRAINT PK_Contact__ContractID PRIMARY KEY (ContactID)
);
CREATE TABLE dbo.KeySkill
(
KeySkillID INT IDENTITY (1, 1) NOT NULL,
Name VARCHAR(50) NOT NULL,
CONSTRAINT PK_KeySkill__KeySkillID PRIMARY KEY (KeySkillID)
);
CREATE TABLE dbo.ContactKeySkill
(
ContactID INT NOT NULL,
KeySkillID INT NOT NULL,
CONSTRAINT PK_ConactKeySkill__ContactID_KeySkillID PRIMARY KEY (ContactID, KeySkillID),
CONSTRAINT FK_ContactKeySill__ContactID FOREIGN KEY (ContactID) REFERENCES dbo.Contact (ContactID),
CONSTRAINT FK_ContactKeySill__KeySkillID FOREIGN KEY (KeySkillID) REFERENCES dbo.KeySkill (KeySkillID)
);
With this structure in place everything else becomes significantly easier. You can recreate your existing format if needed as follows:
SELECT c.ContactID, c.Name, Skills = STRING_AGG(ks.Name, ';')
FROM dbo.Contact AS c
INNER JOIN dbo.ContactKeySkill AS cks
ON cks.ContactID = c.ContactID
INNER JOIN dbo.KeySkill AS ks
ON ks.KeySkillID = cks.KeySkillID
GROUP BY c.ContactID, c.Name;
You are also in complete control of ordering and filtering (with indexes), and data integrity (no duplicates, or typos etc).
Adding/removing skills becomes as simple as inserting/deleting rows rather than having to do any string manipulation.
And if you decided you wanted to rename a skill, e.g. "UI" with "User Interface" well, again that is really really easy in a properly designed database:
UPDATE dbo.KeySkill
SET Name = 'User Interface'
WHERE Name = 'UI';
Because you have now separated all your data, you can be certain that when you update UI there are no side effects because that is the only value stored in that field.
Working Demo on db<>fiddle
If you are not in control of your design and can't make these changes, then the following should work for you:
STUFF(key_skill,
CHARINDEX(CONCAT(';', #current, ';'),CONCAT(';', key_skill, ';')),
LEN(#current),
#replace);
The premise is that if you add ; to the start and the end of both your key_skill string and your #current parameter, then it doesn't matter whether the term is at the start or the end of the string, you would be looking for ;UI; in ;UI;PHP;Building;, so the search term no longer matches in building.
It is easier to use STUFF() here rather than REPLACE(), just so you don't have to actually build a string with semi-colons on the end, then remove them at the end. All you need is to use CHARINDEX to find out where the skill starts in the string (2nd argument in stuff), the length of the skill (3rd argument), and use this as the starting point to "stuff" your new string in (4th argument).
Demo
CREATE TABLE #T (Contact VARCHAR(255), key_skill VARCHAR(255));
INSERT #T(Contact, key_skill)
VALUES
('John Doe', 'AI;UI;ONC;BI;PHP'),
('Craig Smith', 'UI;PHP;Building'),
('Loren Paul', 'AI;UI');
DECLARE #current VARCHAR(50) = 'UI',
#replace VARCHAR(50) = 'New Skill'
UPDATE #T
SET key_skill = STUFF(key_skill,
CHARINDEX(CONCAT(';', #current, ';'),CONCAT(';', key_skill, ';')),
LEN(#current),
#replace)
WHERE CHARINDEX(CONCAT(';', #current, ';'),CONCAT(';', key_skill, ';')) > 0;
SELECT *
FROM #T;
ADENDUM
Since you can't change your data structure a more robust method of doing this will be to deconstruct your delimited list (using STRING_SPLIT()), then make your changes, then reconstruct it again (using STRING_AGG()), e.g.
CREATE TABLE #T (Contact VARCHAR(255), key_skill VARCHAR(255));
INSERT #T(Contact, key_skill)
VALUES
('John Doe', 'AI;UI;ONC;BI;PHP'),
('Craig Smith', 'UI;PHP;Building'),
('Loren Paul', 'AI;UI');
DECLARE #current VARCHAR(50) = 'UI',
#replace VARCHAR(50) = 'New Skill'
UPDATE t
SET t.key_skill = s.NewList
FROM #T AS t
CROSS APPLY
( SELECT STRING_AGG(Value, ';')
FROM ( SELECT Value
FROM STRING_SPLIT(t.key_skill, ';') AS s
WHERE s.value <> #current
UNION
SELECT #replace
WHERE #replace <> ''
) AS s
) AS s (NewList);
Where no #current value is specified this will simply add a skill, and where no #replace is set, then this will just remove the #current.
Working Demo on db<>fiddle
ADENDUM 2
For SQL Server 2016 that doesn't support STRING_AGG() you can use XML extensions as an alternative:
DECLARE #current VARCHAR(50) = 'UI',
#replace VARCHAR(50) = 'New Skill'
UPDATE t
SET t.key_skill = STUFF(s.NewList.value('.', 'NVARCHAR(MAX)'), 1, 1, '')
FROM #T AS t
CROSS APPLY
( SELECT CONCAT(';', Value)
FROM ( SELECT Value
FROM STRING_SPLIT(t.key_skill, ';') AS s
WHERE s.value <> #current
UNION
SELECT #replace
WHERE #replace <> ''
) AS s
FOR XML PATH(''), TYPE
) AS s (NewList);