| (window.webpackJsonp=window.webpackJsonp||[]).push([[521],{916:function(t,s,a){"use strict";a.r(s);var e=a(29),n=Object(e.a)({},(function(){var t=this,s=t._self._c;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"查询补空值"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#查询补空值"}},[t._v("#")]),t._v(" 查询补空值")]),t._v(" "),s("p",[t._v("当执行一些查询时，结果集的某行某列可能没有数据，则此位置结果为空，但这种空值不利于进行数据可视化展示和分析，需要对空值进行填补。")]),t._v(" "),s("p",[t._v("查询补空值允许用户按照特定的方法对任何查询的结果填充空值，如取前一个不为空的值，或线性插值。补空值之后的查询结果能更好地反映数据分布，有利于用户进行数据分析。")]),t._v(" "),s("p",[t._v("在 IoTDB 中，用户可以使用 FILL 子句指定数据缺失的情况下的填充模式。如果查询点不为空，则填充功能将不起作用。")]),t._v(" "),s("h2",{attrs:{id:"填充方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#填充方法"}},[t._v("#")]),t._v(" 填充方法")]),t._v(" "),s("p",[t._v("IoTDB 目前支持 "),s("code",[t._v("previous")]),t._v(" , "),s("code",[t._v("linear")]),t._v(", "),s("code",[t._v("value")]),t._v(" 三种空值填充方式，数据类型和支持的填充方法如下表所示：")]),t._v(" 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false|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:39:00.000+08:00| 22.23| null|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:40:00.000+08:00| 23.43| null|\n+-----------------------------+-------------------------------+--------------------------+\nTotal line number = 4\n")])]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("previous填充后的结果如下：")]),t._v(" "),s("div",{staticClass:"language- line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-text"}},[s("code",[t._v("+-----------------------------+-------------------------------+--------------------------+\n| Time|root.sgcc.wf03.wt01.temperature|root.sgcc.wf03.wt01.status|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:37:00.000+08:00| 21.93| true|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:38:00.000+08:00| 21.93| false|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:39:00.000+08:00| 22.23| false|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:40:00.000+08:00| 23.43| false|\n+-----------------------------+-------------------------------+--------------------------+\nTotal line number = 4\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br")])]),s("blockquote",[s("p",[t._v("注意：如果结果集的某一列第一个值就位空，那我们不会填充这一列，直到遇到这一列第一个不为空的值为止。")])]),t._v(" "),s("h3",{attrs:{id:"linear-填充"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#linear-填充"}},[t._v("#")]),t._v(" Linear 填充")]),t._v(" "),s("p",[t._v("当查询的时间戳下数据为空时，将使用前一个和下一个时间戳的值来填充空白。 语法定义如下：")]),t._v(" "),s("div",{staticClass:"language-sql line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-sql"}},[s("code",[t._v("fill"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("linear"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("在这里，我们举一个使用线性方法填充空值的示例。 SQL 语句如下：")]),t._v(" "),s("div",{staticClass:"language-sql line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-sql"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("select")]),t._v(" temperature "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" root"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"language- line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-text"}},[s("code",[t._v("+-----------------------------+-------------------------------+--------------------------+\n| Time|root.sgcc.wf03.wt01.temperature|root.sgcc.wf03.wt01.status|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:37:00.000+08:00| 21.93| true|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:38:00.000+08:00| 22.08| false|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:39:00.000+08:00| 22.23| null|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:40:00.000+08:00| 23.43| null|\n+-----------------------------+-------------------------------+--------------------------+\nTotal line number = 4\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br")])]),s("blockquote",[s("p",[t._v("注意：如果某个值之前的所有值都为空，或者某个值之后的所有值都为空，我们不会填充该值。\n注意：如果某列的数据类型为boolean/text，我们既不会填充它，也不会报错，只是让那一列保持原样。")])]),t._v(" "),s("h3",{attrs:{id:"value-填充"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#value-填充"}},[t._v("#")]),t._v(" Value 填充")]),t._v(" "),s("p",[t._v("当查询的时间戳下数据为空时，将使用给定的值来填充空白。语法定义如下：")]),t._v(" "),s("div",{staticClass:"language-sql line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-sql"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("select")]),t._v(" temperature "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("from")]),t._v(" root"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sgcc"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("wf03"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("wt01 "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("where")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("time")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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false|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:39:00.000+08:00| 22.23| true|\n+-----------------------------+-------------------------------+--------------------------+\n|2017-11-01T16:40:00.000+08:00| 23.43| true|\n+-----------------------------+-------------------------------+--------------------------+\nTotal line number = 4\n")])]),t._v(" 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