MDEV-29361 Infinite recursive calls when detecting CTE dependencies
This patch resolves the problem of improper name resolution of table references to embedded CTEs for some queries. This improper binding could lead to - infinite sequence of calls of recursive functions - crashes due to resolution of null pointers - wrong result sets returned by queries - bogus error messages If the definition of a CTE contains with clauses then such CTE is called embedding CTE while CTEs from the with clauses are called embedded CTEs. If a table reference used in the definition of an embedded CTE cannot be resolved within the unit that contains this reference it still may be resolved against a CTE definition from the with clause with one of the embedding CTEs. A table reference can be resolved against a CTE definition if it used in the the scope of this definition and it refers to the name of the CTE. Table reference t is in the scope of the CTE definition of CTE cte if - the definition of cte is an element of a with clause declared as RECURSIVE and the reference t belongs either to the unit to which this with clause is attached or to one of the elements of this clause - the definition of cte is an element of a with clause without RECURSIVE specifier and the reference t belongs either to the unit to which this with clause is attached or to one of the elements from this clause that are placed before the definition of cte. If a table reference can be resolved against several CTE definitions then it is bound to the most embedded. The code before this patch not always resolved table references used in embedded CTE according to the above rules. Approved by Oleksandr Byelkin <sanja@mariadb.com>
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