- Correlated and non-correlated.
Non-correlated
Correlated
The inner query doesn't depend on the outer query.
Inner query depends on the outer query.
Can run as a standalone query.
Can't run as a standalone query.
Executed only once.
Executed once for each row selected in the outer query.
Executed before the outer query.
Executed after the outer query.
Can't be used instead of JOIN on the outer query.
Can be used instead of JOIN on the outer query, but will be slower than a JOIN.
- SELECT, WHERE, FROM, INSERT, UPDATE, and DELETE clauses.
- SELECT and WHERE clauses.
- A container for a single SQL statement that will allow you to query a temporary result set.
- Recursive and non-recursive.
- Locking is what happens when a query runs against a database.
- With an index hint.
- READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ...
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