#SQL

I need to analyse and improve the performance on some old SQL statements.

One statement uses NVL in the WHERE clause (no wonder why it's slow) but I still have to improve the performance and the data really needs to be the same when returned.

SELECT *
FROM TOURHead, TOURFIND, SGNRFIND, TNRHead
WHERE TOURHead.cl = '123'
AND TOURHead.cl = TOURFIND.cl
AND TOURHead.TOURNR = TOURFIND.TOURNR
AND TOURFIND.cl =* SGNRFIND.cl
AND TOURFIND.SGNR    =* SGNRFIND.SGNR
AND TOURFIND.cl = TNRHead.cl
AND NVL(TOURFIND.TNR, SGNRFIND.TNR) = TNRHead.TNR;

Really hope someone can help me with this one.

How can I remove UNIQUE NOT NULL from an existing column via DDL?

I currently have a table in production that was originally created via DDL, where the column was defined as UNIQUE NOT NULL:

CREATE TABLE database.Books ( ID %Library.UniqueIdentifier PRIMARY KEY, TagExternal VARCHAR('') UNIQUE NOT NULL,  

I now need to change this column so that it is no longer UNIQUE and no longer NOT NULL, making it equivalent to:

TagExternal VARCHAR(''),

We have a large, existing production taking a feed from a single up-stream system and sending to a wide-variety of downstream systems. One of the downstream systems has been decommissioned, and we have deleted the classes that implemented the routing/transformations from the namespace, and deleted the components from the production (Wardview and WV Out in the diagram below). We now want to delete the messages associated with those components without deleting the messages associated with any other components.