{"Entry":{"collection":"plan","key":"values-scan","name":"Values Scan","aliases":["T_ValuesScan","Values Scan","ValuesScan"],"metadata":{"aliases":["T_ValuesScan","Values Scan","ValuesScan"],"category":"Scan","content_hash":"f86419b898e1c15b67c5fe40f5d846daadec8fa88bd41311a4f603711d6bc967","derived_content_hash":"77fa40e38cc93beff64b9328d1a4a01f1d6d163dd4015bbb19f901a288b5493f","imported_at":"2026-09-30T00:40:44.275691+08:00","name":"Values Scan","name_zh":"ValuesScan","slug":"values-scan","summary":"Evaluates and scans a VALUES row list."}},"Definition":{"Collection":"plan","Key":"values-scan","SourceDatabase":"center","Version":"18","SourceTable":"plan_node","SourceKey":"values-scan","SourceRevision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","Facts":{"comparison_data":{"initializer":"ExecInitValuesScan","memory_mechanism":"unclassified","node_tag":"T_ValuesScan","parallel_callbacks":[],"partial_modes":[],"strategies":[],"text_names":["Values Scan"]},"comparison_hash":"a0f7ecd83c2ff3883a8f6be3d13bd28e040a53da79545a3140489e6b4a0e75e8","description":["Evaluates and scans a VALUES row list."],"description_zh":"计算并扫描 VALUES 行列表。","description_zh_html":"\u003cp\u003e计算并扫描 VALUES 行列表。\u003c/p\u003e\u003cp\u003e核心节点标识：\u003ccode\u003eT_ValuesScan\u003c/code\u003e；EXPLAIN 名称：\u003ccode\u003eValues Scan\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\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":["Values Scan"],"explain_prefixes":["Parallel","Async"],"facts":[{"label":"Core node tag","value":"T_ValuesScan"},{"label":"Structured EXPLAIN Node Type","value":"Values Scan"},{"label":"Inputs","value":"A list of row expressions"},{"label":"Output","value":"VALUES tuples"},{"label":"Executor initializer","value":"ExecInitValuesScan"},{"label":"Memory mechanism","value":"unclassified"}],"facts_zh":[{"label":"核心节点标签","value":"T_ValuesScan"},{"label":"结构化 EXPLAIN 节点类型","value":"Values Scan"},{"label":"输入","value":"行表达式列表"},{"label":"输出","value":"VALUES 元组"},{"label":"执行器初始化函数","value":"ExecInitValuesScan"},{"label":"内存机制","value":"unclassified"}],"memory":{"description":"This extraction does not assign a universal memory limit or spill policy to this node. 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