Return Regex Matches from a sql query - sql-server

Question

I have a table that stores html templates which contain markup with placeholders in key locations, something like this ...
<div>
<div>{FirstName}</div>
<div>{LastName}</div>
</div>
I want to write a query that returns from the table all of the placeholders used from all rows.
SELECT Template
FROM MyTable
WHERE ????
So for the above example the result I want is ...
{FirstName}
{LastName}
I have seen people using regex in SQL but can't figure out how to only return the matches and not the whole column value.
It's also worth noting that I want a result per match ideally but if I got a comma separated list per row that matched or something that would do.

Answer 1

I would approach this using a numbers table, which are very useful anyway, so if you don't have one, I would consider creating one, but for the sake of a complete answer I will assume you don't have one and can't create one. In such scenarios you can generate a list of numbers on the fly quite easily using:
WITH N1 AS (SELECT N FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n (N)),
N2 (N) AS (SELECT 1 FROM N1 AS N1 CROSS JOIN N1 AS N2),
N3 (N) AS (SELECT 1 FROM N2 AS N1 CROSS JOIN N2 AS N2),
--N4 (N) AS (SELECT 1 FROM N3 AS N1 CROSS JOIN N3 AS N2)
Numbers (Number) AS (SELECT ROW_NUMBER() OVER(ORDER BY N) FROM N3)
SELECT Number
FROM Numbers;
This starts with a table of 10 rows created with a table value constructor (N1), it then joins this table with itself to get a table of 100 rows (N2), then joins N2 to itself to get 10,000 rows (N3), this can be repeated as required, before finally using ROW_NUMBER() to get a sequential number in each row. Aaron Bertrand has done a pretty comprehensive series on generating a set or sequence without loops, and this method comes out on top (as a method of creating the table on the fly).
Once you have this numbers table you can join it to your template to find the position of each "{" using SUBSTRING:
SELECT t.Template,
StartPosition = n.Number
FROM dbo.T
INNER JOIN Numbers n
ON SUBSTRING(t.Template, n.Number, 1) = '{';
With your example this will return 16, and 43. Then you can use CHARINDEX to find the "}" that follows each "{":
SELECT t.Template,
StartPosition = n.Number,
EndPosition = CHARINDEX('}', t.template, n.Number) + 1
FROM dbo.T
INNER JOIN Numbers n
ON SUBSTRING(t.Template, n.Number, 1) = '{';
Then you can use SUBSTRING again to extract the term between each start and end position. So a full working example would be:
DECLARE #T TABLE (Template NVARCHAR(MAX));
INSERT #T (Template)
VALUES ('<div>
<div>{FirstName}</div>
<div>{LastName}</div>
</div>');
WITH N1 AS (SELECT N FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n (N)),
N2 (N) AS (SELECT 1 FROM N1 AS N1 CROSS JOIN N1 AS N2),
N3 (N) AS (SELECT 1 FROM N2 AS N1 CROSS JOIN N2 AS N2),
--N4 (N) AS (SELECT 1 FROM N3 AS N1 CROSS JOIN N3 AS N2)
Numbers (Number) AS (SELECT ROW_NUMBER() OVER(ORDER BY N) FROM N3)
SELECT t.Template,
StartPosition = n.Number,
EndPosition = CHARINDEX('}', t.template, n.Number) + 1,
Term = SUBSTRING(t.template, n.Number, CHARINDEX('}', t.template, n.Number) + 1 - n.Number)
FROM #T t
INNER JOIN Numbers n
ON SUBSTRING(t.Template, n.Number, 1) = '{';

Answer 2

See this:
CREATE TABLE #temp(id int identity(1,1), template nvarchar(max))
INSERT INTO #temp(template)
SELECT REPLICATE(N'<div>
<div>{FirstName}</div>
<div>{LastName}</div>
</div>',1000)
;WITH cte AS(
SELECT id,
SUBSTRING(template,CHARINDEX(N'{',template),CHARINDEX(N'}',template)-CHARINDEX(N'{',template)+1) as match,
SUBSTRING(template,CHARINDEX(N'}',template)+1,LEN(template)) as templateRest
FROM #temp
UNION ALL
SELECT id,
SUBSTRING(templateRest,CHARINDEX(N'{',templateRest),CHARINDEX(N'}',templateRest)-CHARINDEX(N'{',templateRest)+1) as match,
SUBSTRING(templateRest,CHARINDEX(N'}',templateRest)+1,LEN(templateRest)) as templateRest
FROM cte
WHERE templateRest LIKE N'%}%'
)
SELECT t.id, t.template, c.match
-- Only distinctive:
-- SELECT DISTINCT t.id, t.template c.match
FROM cte AS c
INNER JOIN #temp AS t
ON c.id = t.id
OPTION(MAXRECURSION 1000) -- if needed, this value could still be raised
DROP TABLE #temp
GO
You can filter it for the template and retrieve all matches.