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 ExtractRaw
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{
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    using ExpectChars = PODArrayWithStackMemory<char, 64>;
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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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        ExpectChars expects_end;
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        UInt8 current_expect_end = 0;
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        for (const auto * extract_begin = pos; pos != end; ++pos)
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        {
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            if (current_expect_end && *pos == current_expect_end)
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            {
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                expects_end.pop_back();
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                current_expect_end = expects_end.empty() ? 0 : expects_end.back();
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            }
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            else if (current_expect_end == '"')
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            {
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                /// skip backslash
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                if (*pos == '\\' && pos + 1 < end && pos[1] == '"')
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                    ++pos;
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            }
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            else
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            {
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                switch (*pos)
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                {
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                    case '[':
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                        current_expect_end = ']';
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                        expects_end.push_back(current_expect_end);
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                        break;
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                    case '{':
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                        current_expect_end = '}';
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                        expects_end.push_back(current_expect_end);
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                        break;
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                    case '"' :
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                        current_expect_end = '"';
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                        expects_end.push_back(current_expect_end);
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                        break;
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                    default:
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                        if (!current_expect_end && (*pos == ',' || *pos == '}'))
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                        {
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                            res_data.insert(extract_begin, pos);
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                            return;
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                        }
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                }
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            }
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        }
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    }
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};
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struct NameSimpleJSONExtractRaw    { static constexpr auto name = "simpleJSONExtractRaw"; };
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using FunctionSimpleJSONExtractRaw = FunctionsStringSearchToString<ExtractParamToStringImpl<ExtractRaw>, NameSimpleJSONExtractRaw>;
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REGISTER_FUNCTION(VisitParamExtractRaw)
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{
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    factory.registerFunction<FunctionSimpleJSONExtractRaw>(FunctionDocumentation{
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        .description = "Returns the value of the field named field_name as a String, including separators.",
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        .syntax = "simpleJSONExtractRaw(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
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        = "It returns the value of the field as a String including separators if the field exists, or an empty String 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":{"def":[1,2,3]}}');
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INSERT INTO jsons VALUES ('{"baz":2}');
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SELECT simpleJSONExtractRaw(json, 'foo') FROM jsons ORDER BY json;)",
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            .result = R"(
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"-4e3"
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-3.4
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{"def":[1,2,3]})"}},
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        .categories{"JSON"}});
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    factory.registerAlias("visitParamExtractRaw", "simpleJSONExtractRaw");
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}
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}
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