{"Entry":{"collection":"plan","key":"recursive-union","name":"Recursive Union","aliases":["Recursive Union","RecursiveUnion","T_RecursiveUnion"],"metadata":{"aliases":["Recursive Union","RecursiveUnion","T_RecursiveUnion"],"category":"Combination","content_hash":"644b31619c32148a2975b5d3f69bf1cb22484977db35fe1c5f2f7ee32bd431fb","derived_content_hash":"6a35e12ac0e7eea63e2daa90486a88f1a99c8f27cd02101db4478d0fc433cf20","imported_at":"2026-09-30T00:40:44.054849+08:00","name":"Recursive Union","name_zh":"RecursiveUnion","slug":"recursive-union","summary":"Executes the non-recursive and recursive terms of a recursive union using working and intermediate tables."}},"Definition":{"Collection":"plan","Key":"recursive-union","SourceDatabase":"center","Version":"18","SourceTable":"plan_node","SourceKey":"recursive-union","SourceRevision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","Facts":{"comparison_data":{"initializer":"ExecInitRecursiveUnion","memory_mechanism":"tuplestore","node_tag":"T_RecursiveUnion","parallel_callbacks":[],"partial_modes":[],"strategies":[],"text_names":["Recursive Union"]},"comparison_hash":"483291c3112fd1d9f34701a541efd658b64074aa0300e044d5e96c65ca8e9023","description":["Executes the non-recursive and recursive terms of a recursive union using working and intermediate tables."],"description_zh":"使用工作表和中间表执行递归 UNION 的非递归项与递归项。","description_zh_html":"\u003cp\u003e使用工作表和中间表执行递归 UNION 的非递归项与递归项。\u003c/p\u003e\u003cp\u003e核心节点标识：\u003ccode\u003eT_RecursiveUnion\u003c/code\u003e；EXPLAIN 名称：\u003ccode\u003eRecursive Union\u003c/code\u003e。\u003c/p\u003e\u003cp\u003e本版本源码中的并行执行或观测回调：该节点实现中未提取到此类回调。回调的存在不表示该节点必然支持共享并行扫描；在并行工作进程中执行也不等于具有并行感知能力。\u003c/p\u003e\u003cp\u003e该节点使用受 \u003ccode\u003ework_mem\u003c/code\u003e 影响的元组存储，必要时可将存储的元组写入临时文件。这并不表示 \u003ccode\u003ework_mem\u003c/code\u003e 限制了该节点的所有内存分配。\u003c/p\u003e\u003ch3\u003e同版本中文手册节选\u003c/h3\u003e\u003cp\u003e\n\u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 会为收到的每个查询制定一个\u003cem class=\"firstterm\"\u003e查询计划\u003c/em\u003e。选择与查询结构和数据特性相匹配的正确计划，对获得良好的性能至关重要，因此系统内置了一个复杂的\u003cem class=\"firstterm\"\u003e规划器\u003c/em\u003e来尽量选出好的计划。可以使用 \u003ca class=\"link\" href=\"/zh/docs/18/sql-explain.html\"\u003e\u003ccode class=\"command\"\u003eEXPLAIN\u003c/code\u003e\u003c/a\u003e 命令查看规划器为任意查询生成的查询计划。读懂计划是一门需要经验积累的技能，本节将尝试介绍其中的基础知识。\n   \u003c/p\u003e\u003cp\u003e\n    本节中的示例取自执行过 \u003ccode class=\"command\"\u003eVACUUM ANALYZE\u003c/code\u003e 的回归测试数据库，使用的是 v18 开发版本源码。如果自行尝试这些示例，通常应当能得到相近的结果，但估计代价和行计数可能略有差异，因为 \u003ccode class=\"command\"\u003eANALYZE\u003c/code\u003e 生成的统计信息来自随机采样而非精确计数，而且代价本身在某种程度上也依赖于平台。\n   \u003c/p\u003e\u003cp\u003e\n    这些示例使用 \u003ccode class=\"command\"\u003eEXPLAIN\u003c/code\u003e 默认的\u003cspan class=\"quote\"\u003e“\u003cspan class=\"quote\"\u003etext\u003c/span\u003e”\u003c/span\u003e输出格式，它紧凑且便于人工阅读。如果希望将 \u003ccode class=\"command\"\u003eEXPLAIN\u003c/code\u003e 的输出交给程序做进一步分析，则应改用机器可读的输出格式（XML、JSON 或 YAML）。\n   \u003c/p\u003e\u003cp\u003e\u003ca href=\"/zh/docs/18/using-explain.html\"\u003e查看完整中文手册与上下文\u003c/a\u003e。\u003c/p\u003e\u003cp\u003e本页开头的中文说明为 PG.CENTER 对编辑说明的翻译；手册节选保留对应版本中文文档原文。源码信息及手册示例不代表重新进行过运行测试。\u003c/p\u003e","evidence_kind":"source and documentation","explain_names":["Recursive Union"],"explain_prefixes":["Parallel","Async"],"facts":[{"label":"Core node tag","value":"T_RecursiveUnion"},{"label":"Structured EXPLAIN Node Type","value":"Recursive Union"},{"label":"Inputs","value":"Non-recursive and recursive child plans"},{"label":"Output","value":"Recursive query tuples"},{"label":"Executor initializer","value":"ExecInitRecursiveUnion"},{"label":"Memory mechanism","value":"tuplestore"}],"facts_zh":[{"label":"核心节点标签","value":"T_RecursiveUnion"},{"label":"结构化 EXPLAIN 节点类型","value":"Recursive Union"},{"label":"输入","value":"非递归和递归子计划"},{"label":"输出","value":"递归查询元组"},{"label":"执行器初始化函数","value":"ExecInitRecursiveUnion"},{"label":"内存机制","value":"tuplestore"}],"memory":{"description":"This node creates a tuplestore with work_mem. 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