Sql:Casting a String to Ids with in Clause

SQL:Casting a String to IDS with IN clause

Op doesn't mention database, so I'll just use SQL Server, because the example SQL in the question looks like TSQL. There are many ways to split string in SQL Server. This article covers the PROs and CONs of just about every method:

"Arrays and Lists in SQL Server 2005 and Beyond, When Table Value Parameters Do Not Cut it" by Erland Sommarskog

You need to create a split function. This is how a split function can be used:

SELECT
    *
    FROM YourTable                               y
    INNER JOIN dbo.yourSplitFunction(@Parameter) s ON y.ID=s.Value

I prefer the number table approach to split a string in TSQL but there are numerous ways to split strings in SQL Server, see the previous link, which explains the PROs and CONs of each.

For the Numbers Table method to work, you need to do this one time table setup, which will create a table Numbers that contains rows from 1 to 10,000:

SELECT TOP 10000 IDENTITY(int,1,1) AS Number
    INTO Numbers
    FROM sys.objects s1
    CROSS JOIN sys.objects s2
ALTER TABLE Numbers ADD CONSTRAINT PK_Numbers PRIMARY KEY CLUSTERED (Number)

Once the Numbers table is set up, create this split function:

CREATE FUNCTION [dbo].[FN_ListToTable]
(
     @SplitOn  char(1)      --REQUIRED, the character to split the @List string on
    ,@List     varchar(8000)--REQUIRED, the list to split apart
)
RETURNS TABLE
AS
RETURN 
(

    ----------------
    --SINGLE QUERY-- --this will not return empty rows
    ----------------
    SELECT
        ListValue
        FROM (SELECT
                  LTRIM(RTRIM(SUBSTRING(List2, number+1, CHARINDEX(@SplitOn, List2, number+1)-number - 1))) AS ListValue
                  FROM (
                           SELECT @SplitOn + @List + @SplitOn AS List2
                       ) AS dt
                      INNER JOIN Numbers n ON n.Number < LEN(dt.List2)
                  WHERE SUBSTRING(List2, number, 1) = @SplitOn
             ) dt2
        WHERE ListValue IS NOT NULL AND ListValue!=''

);
GO 

You can now easily split a CSV string into a table and join on it or use it however you need, even from within dynamic sql. Here is how to use it from your question:

UPDATE t
    SET Col1=...
    FROM dbo.FN_ListToTable(',','7,15,18') dt
        INNER JOIN TBL_USERS                t ON  CAST(dt.value AS INT)=t.id

How to convert varchar to numeric to use in WHERE clause

You should seriously avoid storing CSV data in your SQL tables, because it represents unnormalized data. That being said, there is a way we can write your query even with CSV data, using a slight correction to the data in @string:

DECLARE @string varchar(25) = '453,454';

SELECT
    FirstName + ' ' + LastName Employee
FROM Employee
WHERE ',' + @string + ',' LIKE '%,' + CONVERT(varchar(10), ID) + ',%';

Demo

The trick here is to convert your input CSV 453,454 into this:

,453,454,

Then, we simply search for %,ID,% in that modified CSV string.

Create an IN clause on the fly

Quoting article Using comma separated value parameter strings in SQL IN clauses:

DECLARE @LIST VARCHAR(200)
SET @LIST = '1,3'
SELECT Id, Descr FROM CSVDemo WHERE Id IN (SELECT * FROM dbo.CSVToTable(@LIST))

SQL Query results WHERE ID IN (@ids) can't convert nvarchar() to int

SQL Server 2016 and later versions

 Declare @ids nvarchar(200) = '123,456';

 Select *
 From Users
 Where ID  IN ( Select Value from STRING_SPLIT ( @ids , ',' ))  

For older versions SQL Server 2005 - 2014

 Declare @ids nvarchar(200) = '123,456'; --<-- Comma delimited list of Client Ids

 Select *
 From Users
 Where ID  IN (
              SELECT  CAST(RTRIM(LTRIM(Split.a.value('.', 'VARCHAR(100)'))) AS INT) IDs
              FROM (
                     SELECT Cast ('<X>' 
                                  + Replace(@ids, ',', '</X><X>') 
                                  + '</X>' AS XML) AS Data
                      ) AS t CROSS APPLY Data.nodes ('/X') AS Split(a) 
                    )

Convert a string to int using sql query

You could use CAST or CONVERT:

SELECT CAST(MyVarcharCol AS INT) FROM Table

SELECT CONVERT(INT, MyVarcharCol) FROM Table

Prevent mysql casting string to int in where clause

You should be able to avoid this scenario altogether, but if you wanted a workaround you could concat a character to the front of the string, something like:

SELECT delivery_name 
FROM orders 
WHERE CONCAT('a',orders_id) = CONCAT('a','985225a')

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