An Efficient Way to Check for Existence of Multiple Values in SQL

Using EXISTS (or NOT EXISTS) instead of COUNT() is both a well-know technique among trained DBAs and people with relational database experience, and something I rarely see developers use. I often rewrite existence or duplicate checking queries to eliminate the COUNT() and replace with EXISTS.<p>The author uses SELECT 1 in the example. The usual idiom is SELECT *, and query planners recognize EXISTS (SELECT * ...) and don&#x27;t actually select any columns.