Relational database management systems and the SQL language itself do not have any built-in mechanisms for storing and managing hierarchical structures. There are several different ways to represent trees in relational databases. This paper considers the method of modeling hierarchical data structures in the form of Adjacency Lists and Closure Tables. For each method, there are examples of writing queries to solve typical problems encountered when working with tree structures: finding all descendant leaves, all descendants and ancestors of a given leaf, moving a leaf to another ancestor leaf, and deleting leaves with all its descendants. The possibility of using recursive queries when displaying the entire tree in the Adjacency List model is considered. If the depth of the tree is not known, or it is not known at what level the specified element is, the query can not be built by standard means of the SELECT statement, then you need to create a recursive procedure, or write a recursive query. In order to avoid recursion when outputting the whole tree, all nodes of the subtree, and finding the path from a certain place to the root, the modeling of hierarchical data structures is perf
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