I can consistently get TOAD v5.x Alter Table to fail. The same Alter Table works fine in v4.6.
It’s simple - try changing a column type. I recently tried to change a column type in a COMPLETELY EMPTY BRAND NEW table from Int to BigInt (a foreign key constraint on an already established table required me to do so). It hemmed. It hawed. It muttered for about a minute. It flashed the screen. It changed to the script tab. It thought. Then it thought some more. Somewhere between 3 and 5 minutes after clicking on the OK button, it popped up a message stating “no changes detected.” Grr!
I then went into 4.6, made the same change, and in about 0.25 seconds, it flashed up a message saying “Table altered successfully.” Which brings me to point 2: v5.x alter table statements run WAY slower than v4.6.
There are other ways to get it to fail, too - but I don’t remember them right now. Sorry.
I’m not sure what the problem is, but it would be nice if v5.x’s (the problem exists in both 5.0 and 5.5) alter table’s ran as quickly and reliably as v4.6’s.