Question

I would like to think of myself as a decent SQL Server programmer but this query always stumps me. I’m sure there is a much better way to query this.

SELECT DISTINCT
    database_name,
    CASE 
        WHEN ((SELECT MAX(1) FROM dbo.column_list WHERE column_list IS NOT NULL and database_id = d.database_id) = 1 
                OR (SELECT MAX(1) FROM dbo.table_list WHERE table_list IS NOT NULL and database_id = d.database_id) = 1) 
            THEN 1 
            ELSE 0 
    END AS 'has_definition'
FROM dbo.database_list d;

I have 3 tables database_list, table_list and a column_list. I’m trying to query for a given database in the database list to see if any of the underlying table or column has definitions in them. This query works now and returns a unique list of databases and a has_definition but this seems wrong to me.

Any thoughts would be helpful.

Answer 1

You might try this version instead:

SELECT database_name,
    CASE WHEN EXISTS 
    (
      SELECT 1 FROM dbo.column_list 
         WHERE column_list IS NOT NULL and database_id = d.database_id
      UNION ALL
      SELECT 1 FROM dbo.table_list 
         WHERE table_list IS NOT NULL and database_id = d.database_id
    ) 
            THEN 1 
            ELSE 0 
    END AS [has_definition]
FROM dbo.database_list AS d;

And maybe compare it to this:

SELECT database_name,
    CASE WHEN EXISTS 
    (
      SELECT 1 FROM dbo.column_list 
         WHERE column_list IS NOT NULL and database_id = d.database_id
    ) 
    OR EXISTS
    (
      SELECT 1 FROM dbo.table_list 
         WHERE table_list IS NOT NULL and database_id = d.database_id
    ) 
            THEN 1 
            ELSE 0 
    END AS [has_definition]
FROM dbo.database_list AS d;

I don’t think you’ll need the distinct unless you really have duplicates in dbo.database_list.

Also please don’t use 'single quotes' for aliases – this syntax is deprecated, you should use [square brackets] instead.