Question

The question may not exactly describe what I’d like to do, but I have a stored procedure that has a query returning the following columns

ID Title Tablename

The Title is currently being returned as NULL as I need to be able to get it from a JOINED table referenced in the Tablename column. There could be several different Tablename values returned in the query and the Title for each record needs to be got from the Table referenced in the Tablename field for each record.

Is there a pure SQL way of doing this?

I’ve thought about creating a temporary table and then looping through each record and setting the Title by running a seperate query against the table in Tablename, but am hopign for a cleaner solution.

Thanks

Answer 1

This may be an indication of a design not directly suited to SQL. What is the reason that your Title information is stored in multiple table? Can it be re-factored to not be so?

If, however, the list of tables is a fixed list, there is a solution; use UNION ALL in a view, or CTE to use an in-line view, to make your many tables look like one table…

WITH
  inlineView
AS
(
              SELECT 'table1' AS tableName, x, y, z, title FROM table1
  UNION ALL   SELECT 'table2' AS tableName, x, y, z, title FROM table2
  UNION ALL   SELECT 'table3' AS tableName, x, y, z, title FROM table3
)
SELECT
  *
FROM
  aTable
INNER JOIN
  inlineView
    ON  aTable.tableName = inlineView.tableName
    AND aTable.x         = inlineView.x

If you can’t make it fit that, or the number of tables you need to include in the view is not fixed, you will probably need a loop and some dynamic SQL. Again, a strong indicator that the schema isn’t really SQL friendly.