ClickHouse/src/Interpreters/InterpreterExplainQuery.cpp

#include <Interpreters/InterpreterExplainQuery.h>

#include <DataStreams/BlockIO.h>
#include <DataStreams/OneBlockInputStream.h>
#include <DataTypes/DataTypeString.h>
#include <Interpreters/InDepthNodeVisitor.h>
#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/Context.h>
#include <Parsers/DumpASTNode.h>
#include <Parsers/queryToString.h>
#include <Parsers/ASTExplainQuery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/ASTSelectQuery.h>
#include <IO/WriteBufferFromOStream.h>

#include <Storages/StorageView.h>
#include <sstream>
#include <Processors/QueryPlan/QueryPlan.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int INCORRECT_QUERY;
}

namespace
{
    struct ExplainAnalyzedSyntaxMatcher
    {
        struct Data
        {
            const Context & context;
        };

        static bool needChildVisit(ASTPtr & node, ASTPtr &)
        {
            return !node->as<ASTSelectQuery>();
        }

        static void visit(ASTPtr & ast, Data & data)
        {
            if (auto * select = ast->as<ASTSelectQuery>())
                visit(*select, ast, data);
        }

        static void visit(ASTSelectQuery & select, ASTPtr & node, Data & data)
        {
            InterpreterSelectQuery interpreter(
                node, data.context, SelectQueryOptions(QueryProcessingStage::FetchColumns).analyze().modify());

            const SelectQueryInfo & query_info = interpreter.getQueryInfo();
            if (query_info.view_query)
            {
                ASTPtr tmp;
                StorageView::replaceWithSubquery(select, query_info.view_query->clone(), tmp);
            }
        }
    };

    using ExplainAnalyzedSyntaxVisitor = InDepthNodeVisitor<ExplainAnalyzedSyntaxMatcher, true>;

}

BlockIO InterpreterExplainQuery::execute()
{
    BlockIO res;
    res.in = executeImpl();
    return res;
}


Block InterpreterExplainQuery::getSampleBlock()
{
    Block block;

    ColumnWithTypeAndName col;
    col.name = "explain";
    col.type = std::make_shared<DataTypeString>();
    col.column = col.type->createColumn();
    block.insert(col);

    return block;
}

static void fillColumn(IColumn & column, const std::string & str)
{
    size_t start = 0;
    size_t end = 0;
    size_t size = str.size();

    while (end < size)
    {
        if (str[end] == '\n')
        {
            column.insertData(str.data() + start, end - start);
            start = end + 1;
        }

        ++end;
    }

    if (start < end)
        column.insertData(str.data() + start, end - start);
}

BlockInputStreamPtr InterpreterExplainQuery::executeImpl()
{
    const auto & ast = query->as<ASTExplainQuery &>();

    Block sample_block = getSampleBlock();
    MutableColumns res_columns = sample_block.cloneEmptyColumns();

    std::stringstream ss;

    if (ast.getKind() == ASTExplainQuery::ParsedAST)
    {
        dumpAST(ast, ss);
    }
    else if (ast.getKind() == ASTExplainQuery::AnalyzedSyntax)
    {
        ExplainAnalyzedSyntaxVisitor::Data data{.context = context};
        ExplainAnalyzedSyntaxVisitor(data).visit(query);

        ast.children.at(0)->format(IAST::FormatSettings(ss, false));
    }
    else if (ast.getKind() == ASTExplainQuery::QueryPlan)
    {
        if (!dynamic_cast<const ASTSelectWithUnionQuery *>(ast.getExplainedQuery().get()))
            throw Exception("Only SELECT is supported for EXPLAIN query", ErrorCodes::INCORRECT_QUERY);

        QueryPlan plan;

        InterpreterSelectWithUnionQuery interpreter(ast.getExplainedQuery(), context, SelectQueryOptions());
        interpreter.buildQueryPlan(plan);

        WriteBufferFromOStream buffer(ss);
        plan.explain(buffer);
    }

    fillColumn(*res_columns[0], ss.str());

    return std::make_shared<OneBlockInputStream>(sample_block.cloneWithColumns(std::move(res_columns)));
}

}