ClickHouse

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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionsVisitParam.h>
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#include <Functions/FunctionsStringSearch.h>
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namespace DB
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{
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struct NameSimpleJSONExtractFloat { static constexpr auto name = "simpleJSONExtractFloat"; };
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using FunctionSimpleJSONExtractFloat = FunctionsStringSearch<ExtractParamImpl<NameSimpleJSONExtractFloat, ExtractNumericType<Float64>>>;
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REGISTER_FUNCTION(VisitParamExtractFloat)
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{
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    factory.registerFunction<FunctionSimpleJSONExtractFloat>(FunctionDocumentation{
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        .description
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        = "Parses Float64 from the value of the field named field_name. If this is a string field, it tries to parse a number from the "
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          "beginning of the string. If the field does not exist, or it exists but does not contain a number, it returns 0.",
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        .syntax = "simpleJSONExtractFloat(json, field_name)",
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        .arguments
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        = {{"json", "The JSON in which the field is searched for. String."},
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           {"field_name", "The name of the field to search for. String literal."}},
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        .returned_value = "It returns the number parsed from the field if the field exists and contains a number, 0 otherwise.",
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        .examples
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        = {{.name = "simple",
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            .query = R"(CREATE TABLE jsons
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(
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    json String
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)
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ENGINE = Memory;
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INSERT INTO jsons VALUES ('{"foo":"-4e3"}');
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INSERT INTO jsons VALUES ('{"foo":-3.4}');
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INSERT INTO jsons VALUES ('{"foo":5}');
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INSERT INTO jsons VALUES ('{"foo":"not1number"}');
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INSERT INTO jsons VALUES ('{"baz":2}');
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SELECT simpleJSONExtractFloat(json, 'foo') FROM jsons ORDER BY json;)",
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            .result = R"(0
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-4000
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0
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-3.4
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5)"}},
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        .categories{"JSON"}});
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    factory.registerAlias("visitParamExtractFloat", "simpleJSONExtractFloat");
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}
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}
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