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For information about functions available in SQL, refer to the\n",(0,i.yg)("a",{parentName:"p",href:"/docs/29.0.0/querying/sql-aggregations"},"SQL documentation"),".")),(0,i.yg)("p",null,"Post-aggregations are specifications of processing that should happen on aggregated values as they come out of Apache Druid. If you include a post aggregation as part of a query, make sure to include all aggregators the post-aggregator requires."),(0,i.yg)("p",null,"There are several post-aggregators available."),(0,i.yg)("h3",{id:"arithmetic-post-aggregator"},"Arithmetic post-aggregator"),(0,i.yg)("p",null,"The arithmetic post-aggregator applies the provided function to the given\nfields from left to right. 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",(0,i.yg)("inlineCode",{parentName:"td"},"numericFirst")," ordering always returns finite values first, followed by ",(0,i.yg)("inlineCode",{parentName:"td"},"NaN"),", and infinite values last."),(0,i.yg)("td",{parentName:"tr",align:null},"No")))),(0,i.yg)("p",null,(0,i.yg)("strong",{parentName:"p"},"Note"),":"),(0,i.yg)("ul",null,(0,i.yg)("li",{parentName:"ul"},(0,i.yg)("inlineCode",{parentName:"li"},"/")," division always returns ",(0,i.yg)("inlineCode",{parentName:"li"},"0")," if dividing by",(0,i.yg)("inlineCode",{parentName:"li"},"0"),", regardless of the numerator."),(0,i.yg)("li",{parentName:"ul"},(0,i.yg)("inlineCode",{parentName:"li"},"quotient")," division behaves like regular floating point division"),(0,i.yg)("li",{parentName:"ul"},"Arithmetic post-aggregators always use floating point arithmetic.")),(0,i.yg)("p",null,"Example:"),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  "type"  : "arithmetic",\n  "name"  : "mult",\n  "fn"    : "*",\n  "fields": [\n    {"type": "fieldAccess", "fieldName":  "someAgg"},\n    {"type": "fieldAccess", "fieldName":  "someOtherAgg"}\n  ]\n}\n')),(0,i.yg)("h3",{id:"field-accessor-post-aggregators"},"Field accessor post-aggregators"),(0,i.yg)("p",null,"These post-aggregators return the value produced by the specified ",(0,i.yg)("a",{parentName:"p",href:"/docs/29.0.0/querying/dimensionspecs"},"dimension")," or ",(0,i.yg)("a",{parentName:"p",href:"/docs/29.0.0/querying/aggregations"},"aggregator"),"."),(0,i.yg)("table",null,(0,i.yg)("thead",{parentName:"table"},(0,i.yg)("tr",{parentName:"thead"},(0,i.yg)("th",{parentName:"tr",align:null},"Property"),(0,i.yg)("th",{parentName:"tr",align:null},"Description"),(0,i.yg)("th",{parentName:"tr",align:null},"Required"))),(0,i.yg)("tbody",{parentName:"table"},(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"type")),(0,i.yg)("td",{parentName:"tr",align:null},"Must be ",(0,i.yg)("inlineCode",{parentName:"td"},'"fieldAccess"')," or ",(0,i.yg)("inlineCode",{parentName:"td"},'"finalizingFieldAccess"'),". 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These are similar to the\nSQL ",(0,i.yg)("inlineCode",{parentName:"p"},"MAX")," and ",(0,i.yg)("inlineCode",{parentName:"p"},"GREATEST")," functions."),(0,i.yg)("p",null,"Example:"),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  "type"  : "doubleGreatest",\n  "name"  : "theGreatest",\n  "fields": [\n   { "type": "fieldAccess", "fieldName": "someAgg" },\n   { "type": "fieldAccess", "fieldName": "someOtherAgg" }\n  ]\n}\n')),(0,i.yg)("h3",{id:"javascript-post-aggregator"},"JavaScript post-aggregator"),(0,i.yg)("p",null,"Applies the provided JavaScript function to the given fields. Fields are passed as arguments to the JavaScript function in the given order."),(0,i.yg)("table",null,(0,i.yg)("thead",{parentName:"table"},(0,i.yg)("tr",{parentName:"thead"},(0,i.yg)("th",{parentName:"tr",align:null},"Property"),(0,i.yg)("th",{parentName:"tr",align:null},"Description"),(0,i.yg)("th",{parentName:"tr",align:null},"Required"))),(0,i.yg)("tbody",{parentName:"table"},(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"type")),(0,i.yg)("td",{parentName:"tr",align:null},"Must be ",(0,i.yg)("inlineCode",{parentName:"td"},'"javascript"')),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")),(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"name")),(0,i.yg)("td",{parentName:"tr",align:null},"Output name of the post-aggregation"),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")),(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"fieldNames")),(0,i.yg)("td",{parentName:"tr",align:null},"List of input dimension or aggregator output names"),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")),(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"function")),(0,i.yg)("td",{parentName:"tr",align:null},"String javascript function which accepts ",(0,i.yg)("inlineCode",{parentName:"td"},"fieldNames")," as arguments"),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")))),(0,i.yg)("p",null,"Example:"),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  "type": "javascript",\n  "name": "someJavascript",\n  "fieldNames" : ["someAgg", "someOtherAgg"],\n  "function": "function(someAgg, someOtherAgg) { return 100 * Math.abs(someAgg) / someOtherAgg;"\n}\n')),(0,i.yg)("admonition",{type:"info"},(0,i.yg)("p",{parentName:"admonition"}," JavaScript-based functionality is disabled by default. Please refer to the Druid ",(0,i.yg)("a",{parentName:"p",href:"/docs/29.0.0/development/javascript"},"JavaScript programming guide")," for guidelines about using Druid's JavaScript functionality, including instructions on how to enable it.")),(0,i.yg)("h3",{id:"hyperunique-cardinality-post-aggregator"},"HyperUnique Cardinality post-aggregator"),(0,i.yg)("p",null,"The hyperUniqueCardinality post aggregator is used to wrap a hyperUnique object such that it can be used in post aggregations."),(0,i.yg)("table",null,(0,i.yg)("thead",{parentName:"table"},(0,i.yg)("tr",{parentName:"thead"},(0,i.yg)("th",{parentName:"tr",align:null},"Property"),(0,i.yg)("th",{parentName:"tr",align:null},"Description"),(0,i.yg)("th",{parentName:"tr",align:null},"Required"))),(0,i.yg)("tbody",{parentName:"table"},(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"type")),(0,i.yg)("td",{parentName:"tr",align:null},"Must be ",(0,i.yg)("inlineCode",{parentName:"td"},'"hyperUniqueCardinality"')),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")),(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"name")),(0,i.yg)("td",{parentName:"tr",align:null},"Output name of the post-aggregation"),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")),(0,i.yg)("tr",{parentName:"tbody"},(0,i.yg)("td",{parentName:"tr",align:null},(0,i.yg)("inlineCode",{parentName:"td"},"fieldName")),(0,i.yg)("td",{parentName:"tr",align:null},"The output name of a ",(0,i.yg)("a",{parentName:"td",href:"/docs/29.0.0/querying/aggregations#cardinality-hyperunique"},(0,i.yg)("inlineCode",{parentName:"a"},"hyperUnique")," aggregator")),(0,i.yg)("td",{parentName:"tr",align:null},"Yes")))),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  "type"  : "hyperUniqueCardinality",\n  "name": "someCardinality",\n  "fieldName"  : "someHyperunique"\n}\n')),(0,i.yg)("p",null,"It can be used in a sample calculation as so:"),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  ...\n  "aggregations" : [{\n    {"type" : "count", "name" : "rows"},\n    {"type" : "hyperUnique", "name" : "unique_users", "fieldName" : "uniques"}\n  }],\n  "postAggregations" : [{\n    "type"   : "arithmetic",\n    "name"   : "average_users_per_row",\n    "fn"     : "/",\n    "fields" : [\n      { "type" : "hyperUniqueCardinality", "fieldName" : "unique_users" },\n      { "type" : "fieldAccess", "name" : "rows", "fieldName" : "rows" }\n    ]\n  }]\n  ...\n')),(0,i.yg)("p",null,'This post-aggregator will inherit the rounding behavior of the aggregator it references. Note that this inheritance\nis only effective if you directly reference an aggregator. Going through another post-aggregator, for example, will\ncause the user-specified rounding behavior to get lost and default to "no rounding".'),(0,i.yg)("h2",{id:"example-usage"},"Example Usage"),(0,i.yg)("p",null,'In this example, let\u2019s calculate a simple percentage using post aggregators. Let\u2019s imagine our data set has a metric called "total".'),(0,i.yg)("p",null,"The format of the query JSON is as follows:"),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  ...\n  "aggregations" : [\n    { "type" : "count", "name" : "rows" },\n    { "type" : "doubleSum", "name" : "tot", "fieldName" : "total" }\n  ],\n  "postAggregations" : [{\n    "type"   : "arithmetic",\n    "name"   : "average",\n    "fn"     : "/",\n    "fields" : [\n           { "type" : "fieldAccess", "name" : "tot", "fieldName" : "tot" },\n           { "type" : "fieldAccess", "name" : "rows", "fieldName" : "rows" }\n         ]\n  }]\n  ...\n}\n')),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  ...\n  "aggregations" : [\n    { "type" : "doubleSum", "name" : "tot", "fieldName" : "total" },\n    { "type" : "doubleSum", "name" : "part", "fieldName" : "part" }\n  ],\n  "postAggregations" : [{\n    "type"   : "arithmetic",\n    "name"   : "part_percentage",\n    "fn"     : "*",\n    "fields" : [\n       { "type"   : "arithmetic",\n         "name"   : "ratio",\n         "fn"     : "/",\n         "fields" : [\n           { "type" : "fieldAccess", "name" : "part", "fieldName" : "part" },\n           { "type" : "fieldAccess", "name" : "tot", "fieldName" : "tot" }\n         ]\n       },\n       { "type" : "constant", "name": "const", "value" : 100 }\n    ]\n  }]\n  ...\n}\n')),(0,i.yg)("p",null,"The same could be computed using an expression post-aggregator: "),(0,i.yg)("pre",null,(0,i.yg)("code",{parentName:"pre",className:"language-json"},'{\n  ...\n  "aggregations" : [\n    { "type" : "doubleSum", "name" : "tot", "fieldName" : "total" },\n    { "type" : "doubleSum", "name" : "part", "fieldName" : "part" }\n  ],\n  "postAggregations" : [{\n    "type"       : "expression",\n    "name"       : "part_percentage",\n    "expression" : "100 * (part / tot)"\n  }]\n  ...\n}\n')))}u.isMDXComponent=!0}}]);