SQL-99 allows for nested subqueries at nearly all places within a query. From a user's point
of view, nested queries can greatly simplify the formulation of complex queries. However …

Optimizing SQL subqueries has been an active area in database research and the database
industry throughout the last decades. Previous work has already identified some …

Most aggregation queries contain both group-by and join operators, and spend a significant
amount of time evaluating these two expensive operators. Merging them into one operator …

Nested queries are commonly used to express complex use-cases by connecting the output
of a subquery as an input to the outer query block. However, their execution is highly time …

There is provided a computer-implemented method of optimizing a query. An exemplary
method comprises receiving a first query configured to generate a result set. The query may …

Logic bugs are bugs that can cause database management systems (DBMSs) to silently
produce incorrect results for given queries. Such bugs are severe, because they can easily …

A key promise of SQL is that the optimizer will find the most efficient execution plan,
regardless of how the query is formulated. In general, query optimizers of modern database …

Data-centric systems play a crucial role in computer systems, and their correctness is of
paramount importance. Logic bugs are one of the main types of bugs in data-centric …

We propose a logical framework to analyze complex predicates (those involving a subquery)
in SQL. We propose a new operator in the relational algebra for handling such predicates …

The following thesis presents novel optimization methods for structured and semi-structured
databases. Developed methods are based on query rewriting and focus on reduction of …