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LibSQL: Implement a DESCRIBE TABLE statement

This statement (for now) outputs the name and types of the different
attributes in a table. It's not standard SQL but all DBMSs that I know
of implement a sort of statement for such functionality.

Since the output of DESCRIBE TABLE is just a relation, an internal
schema, `master` was created and a table definition for DESCRIBE into
it. The table definition and the master schema are not accessible by the
user.
This commit is contained in:
Mahmoud Mandour 2021-12-06 15:30:38 +02:00 committed by Andreas Kling
parent cd4dba87fa
commit f6233913ad
9 changed files with 93 additions and 0 deletions

View file

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/*
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibSQL/AST/AST.h>
#include <LibSQL/Database.h>
#include <LibSQL/Meta.h>
#include <LibSQL/Row.h>
namespace SQL::AST {
RefPtr<SQLResult> DescribeTable::execute(ExecutionContext& context) const
{
auto schema_name = m_qualified_table_name->schema_name();
auto table_name = m_qualified_table_name->table_name();
auto table_def_or_error = context.database->get_table(schema_name, table_name);
auto table_def = table_def_or_error.release_value();
if (!table_def) {
if (schema_name.is_null() || schema_name.is_empty())
schema_name = "default";
return SQLResult::construct(SQLCommand::Describe, SQLErrorCode::TableDoesNotExist, String::formatted("{}.{}", schema_name, table_name));
}
auto describe_table_def = context.database->get_table("master", "internal_describe_table").value();
NonnullRefPtr<TupleDescriptor> descriptor = describe_table_def->to_tuple_descriptor();
context.result = SQLResult::construct();
for (auto& column : table_def->columns()) {
Tuple tuple(descriptor);
tuple[0] = column.name();
tuple[1] = SQLType_name(column.type());
context.result->insert(tuple, Tuple {});
}
return context.result;
}
}