ClickHouse

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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionsVisitParam.h>
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#include <Functions/FunctionsStringSearchToString.h>
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namespace DB
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{
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struct ExtractString
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{
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    static void extract(const UInt8 * pos, const UInt8 * end, ColumnString::Chars & res_data)
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    {
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        size_t old_size = res_data.size();
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        ReadBufferFromMemory in(pos, end - pos);
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        if (!tryReadJSONStringInto(res_data, in, default_json_settings))
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            res_data.resize(old_size);
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    }
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    static const FormatSettings::JSON constexpr default_json_settings;
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};
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struct NameSimpleJSONExtractString { static constexpr auto name = "simpleJSONExtractString"; };
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using FunctionSimpleJSONExtractString = FunctionsStringSearchToString<ExtractParamToStringImpl<ExtractString>, NameSimpleJSONExtractString>;
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REGISTER_FUNCTION(VisitParamExtractString)
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{
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    factory.registerFunction<FunctionSimpleJSONExtractString>(FunctionDocumentation{
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        .description = R"(Parses String in double quotes from the value of the field named field_name.
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        There is currently no support for code points in the format \uXXXX\uYYYY that are not from the basic multilingual plane (they are converted to CESU-8 instead of UTF-8).)",
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        .syntax = "simpleJSONExtractString(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 value of a field as a String, including separators. The value is unescaped. It returns an empty "
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                          "String: if the field doesn't contain a double quoted string, if unescaping fails or if the field doesn't exist.",
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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":"\\n\\u0000"}');
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INSERT INTO jsons VALUES ('{"foo":"\\u263"}');
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INSERT INTO jsons VALUES ('{"foo":"\\u263a"}');
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INSERT INTO jsons VALUES ('{"foo":"hello}');
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SELECT simpleJSONExtractString(json, 'foo') FROM jsons ORDER BY json;)",
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            .result = R"(\n\0
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☺
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)"}},
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        .categories{"JSON"}});
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    factory.registerAlias("visitParamExtractString", "simpleJSONExtractString");
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}
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}
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