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I'm using the pg gem to talk to PostgreSQL from Ruby. Is there a
better way to check if there are no results than using res.ntuples == 0?
conn = PGconn.connect config
cmd = "select * from labels inner join labels_mail using(label_id) " +
"where labels_mail.mail_id = $1 and labels.name = $2"
res = conn.exec(cmd, [mail_id, mailbox])
if res.ntuples == 0 # <=== is there a better way to check this?
cmd = "insert into labels_mail (mail_id, label_id) values ($1, $2)"
conn.exec(cmd, [mail_id, label_id(mailbox)])
end
321
The PostgreSQL NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank. A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different from a zero value or a field that contains spaces.
Example - With SELECT StatementSELECT * FROM employees WHERE first_number IS NULL; This PostgreSQL IS NULL example will return all records from the employees table where the first_name contains a NULL value.
The NVL function returns the first of its arguments that isn't null. NVL evaluates the first expression. If that expression evaluates to NULL , NVL returns the second expression. NVL(expr1, expr2) The return type is the same as the argument types.
Note. <> is the standard SQL notation for “not equal”. !=
ntuples, a typo? It is faster and concise to use zero? than == 0
if res.num_tuples.zero?
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