As others have already mentioned, what the author is calling "explicit" would be more typically called "imperative". I'm going to go further though and say that

As others have already mentioned, what the author is calling "explicit" would be more typically called "imperative". I'm going to go further though and say that I think "explicit" as used here is actually wrong. Take the example from the article: SELECT * FROM users WHERE name = 'jorge' ORDER BY age; and assume that we have exactly one index on the table, namely a compound one on `name, age`. If that index is used, then _only_ the filtering need be done. In SQL, because the execution sequence is left unspecified, we can continue to write the query as is while still allowing the DB to skip the unneeded ordering step (whether it does so or not is a different question obviously). If, however, the execution sequence must be "specified" (cf. "explicit") and you don't want to perform the unnecessary ordering step, then either the order must be left out of the query (and thus implicit), or the DB needs to be able to ignore what you tell it to do.