ClickHouse/src/Interpreters/InterpreterDescribeQuery.cpp

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#include <Storages/IStorage.h>
#include <DataStreams/OneBlockInputStream.h>
#include <DataStreams/BlockIO.h>
#include <DataTypes/DataTypeString.h>
#include <Parsers/queryToString.h>
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#include <Common/typeid_cast.h>
#include <TableFunctions/ITableFunction.h>
#include <TableFunctions/TableFunctionFactory.h>
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#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/Context.h>
#include <Interpreters/InterpreterDescribeQuery.h>
#include <Interpreters/IdentifierSemantic.h>
#include <Access/AccessFlags.h>
#include <Parsers/ASTIdentifier.h>
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#include <Parsers/ASTFunction.h>
#include <Parsers/ASTTablesInSelectQuery.h>
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#include <Parsers/TablePropertiesQueriesASTs.h>
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namespace DB
{
BlockIO InterpreterDescribeQuery::execute()
{
BlockIO res;
res.in = executeImpl();
return res;
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}
Block InterpreterDescribeQuery::getSampleBlock()
{
Block block;
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ColumnWithTypeAndName col;
col.name = "name";
col.type = std::make_shared<DataTypeString>();
col.column = col.type->createColumn();
block.insert(col);
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col.name = "type";
block.insert(col);
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col.name = "default_type";
block.insert(col);
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col.name = "default_expression";
block.insert(col);
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col.name = "comment";
block.insert(col);
col.name = "codec_expression";
block.insert(col);
col.name = "ttl_expression";
block.insert(col);
return block;
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}
BlockInputStreamPtr InterpreterDescribeQuery::executeImpl()
{
ColumnsDescription columns;
const auto & ast = query_ptr->as<ASTDescribeQuery &>();
const auto & table_expression = ast.table_expression->as<ASTTableExpression &>();
if (table_expression.subquery)
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{
auto names_and_types = InterpreterSelectWithUnionQuery::getSampleBlock(
table_expression.subquery->children.at(0), context).getNamesAndTypesList();
columns = ColumnsDescription(std::move(names_and_types));
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}
else
{
StoragePtr table;
if (table_expression.table_function)
{
const auto & table_function = table_expression.table_function->as<ASTFunction &>();
TableFunctionPtr table_function_ptr = TableFunctionFactory::instance().get(table_function.name, context);
/// Run the table function and remember the result
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table = table_function_ptr->execute(table_expression.table_function, context, table_function_ptr->getName());
}
else
{
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auto table_id = context.resolveStorageID(table_expression.database_and_table_name);
context.checkAccess(AccessType::SHOW_COLUMNS, table_id);
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table = DatabaseCatalog::instance().getTable(table_id, context);
}
auto table_lock = table->lockStructureForShare(
false, context.getInitialQueryId(), context.getSettingsRef().lock_acquire_timeout);
columns = table->getColumns();
}
Block sample_block = getSampleBlock();
MutableColumns res_columns = sample_block.cloneEmptyColumns();
for (const auto & column : columns)
{
res_columns[0]->insert(column.name);
res_columns[1]->insert(column.type->getName());
if (column.default_desc.expression)
{
res_columns[2]->insert(toString(column.default_desc.kind));
res_columns[3]->insert(queryToString(column.default_desc.expression));
}
else
{
res_columns[2]->insertDefault();
res_columns[3]->insertDefault();
}
res_columns[4]->insert(column.comment);
if (column.codec)
res_columns[5]->insert(column.codec->getCodecDesc());
else
res_columns[5]->insertDefault();
if (column.ttl)
res_columns[6]->insert(queryToString(column.ttl));
else
res_columns[6]->insertDefault();
}
return std::make_shared<OneBlockInputStream>(sample_block.cloneWithColumns(std::move(res_columns)));
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}
}