use select parameter in subquery as column value - tsql

Question

I'm trying to set the columnName, databaseName, schemaName etc. dynamically based on a temporary table but cant seem to make it work. i've tried below?
Create Table #test(databaseName varchar(128), schemaName varchar(128), columnName varchar(128), datatypeName varchar(128));
INSERT INTO #test ('testDatabase', 'testSchema', 'testTable', 'priceColumn');
SELECT
Case
WHEN DataType = 'int'
THEN SELECT MAX(ColumnName) FROM Concat(databaseName, '.', schemaName, '.', tableName)
ELSE 0
end
FROM #test;
DROP TABLE #test;
the expected result is that this below subquery take each line in the row in #test table and then query based on these values so it return the maxPrice from that table
SELECT MAX(ColumnName) FROM Concat(databaseName, '.', schemaName, '.', tableName)

Answer 1

Are you trying to aggregate on a calculated field while preserving the query flow?
You can try something like this.
SELECT
MAX(FullName)
FROM
(
SELECT
FullName = databaseName+ '.' + schemaName + '.' + columnName,
*
FROM
#test
) AS A
WHERE
DataTypeName='int'
Another example
SELECT
MAX(FullNameInt),
MAX(FullNameOther)
FROM
(
SELECT
FullNameInt = CASE WHEN DataTypeName='int' THEN databaseName+ '.' + schemaName + '.' + columnName ELSE NULL END,
FullNameOther = CASE WHEN DataTypeName<>'int' THEN databaseName+ '.' + schemaName + '.' + columnName ELSE NULL END,
*
FROM
#test
) AS A