This was pretty easy to find, but considering how unexpected it is, I feel it's worth a mention.
There are no empty strings in Oracle's SQL or PL/SQL.
Consider -
myVar VARCHAR2(10) := '';
The following will never execute.
IF myVar = '' THEN -- do something END IF;
myVar must be compared to NULL for the block to work.
IF myVar IS NULL -- do something END IF;
Likewise
SELECT someField FROM someTable WHERE someField = '';Will always return 0 rows.
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