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LibSQL: Implement a DESCRIBE TABLE statement

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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
Notes: sideshowbarker 2024-07-17 19:47:13 +09:00 
Author: https://github.com/i3abghany
Commit: https://github.com/SerenityOS/serenity/commit/f6233913ad4
Pull-request: https://github.com/SerenityOS/serenity/pull/10371
Reviewed-by: https://github.com/trflynn89 ✅
9 changed files with 93 additions and 0 deletions
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15
Userland/Libraries/LibSQL/AST/AST.h
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@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, Tim Flynn <trflynn89@serenityos.org>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -1050,4 +1051,18 @@ private:
RefPtr<LimitClause> m_limit_clause;
};
class DescribeTable : public Statement {
public:
DescribeTable(NonnullRefPtr<QualifiedTableName> qualified_table_name)
: m_qualified_table_name(move(qualified_table_name))
{
}
NonnullRefPtr<QualifiedTableName> qualified_table_name() const { return m_qualified_table_name; }
RefPtr<SQLResult> execute(ExecutionContext&) const override;
private:
NonnullRefPtr<QualifiedTableName> m_qualified_table_name;
};
}

42
Userland/Libraries/LibSQL/AST/Describe.cpp Normal file
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@ -0,0 +1,42 @@
/*
* 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;
}
}

13
Userland/Libraries/LibSQL/AST/Parser.cpp
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@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, Tim Flynn <trflynn89@serenityos.org>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -46,6 +47,8 @@ NonnullRefPtr<Statement> Parser::parse_statement()
return parse_alter_table_statement();
case TokenType::Drop:
return parse_drop_table_statement();
case TokenType::Describe:
return parse_describe_table_statement();
case TokenType::Insert:
return parse_insert_statement({});
case TokenType::Update:
@ -181,6 +184,16 @@ NonnullRefPtr<DropTable> Parser::parse_drop_table_statement()
return create_ast_node<DropTable>(move(schema_name), move(table_name), is_error_if_table_does_not_exist);
}
NonnullRefPtr<DescribeTable> Parser::parse_describe_table_statement()
{
consume(TokenType::Describe);
consume(TokenType::Table);
auto table_name = parse_qualified_table_name();
return create_ast_node<DescribeTable>(move(table_name));
}
NonnullRefPtr<Insert> Parser::parse_insert_statement(RefPtr<CommonTableExpressionList> common_table_expression_list)
{
// https://sqlite.org/lang_insert.html

2
Userland/Libraries/LibSQL/AST/Parser.h
View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, Tim Flynn <trflynn89@serenityos.org>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -59,6 +60,7 @@ private:
NonnullRefPtr<CreateTable> parse_create_table_statement();
NonnullRefPtr<AlterTable> parse_alter_table_statement();
NonnullRefPtr<DropTable> parse_drop_table_statement();
NonnullRefPtr<DescribeTable> parse_describe_table_statement();
NonnullRefPtr<Insert> parse_insert_statement(RefPtr<CommonTableExpressionList>);
NonnullRefPtr<Update> parse_update_statement(RefPtr<CommonTableExpressionList>);
NonnullRefPtr<Delete> parse_delete_statement(RefPtr<CommonTableExpressionList>);

2
Userland/Libraries/LibSQL/AST/Token.h
View file

@ -1,6 +1,7 @@
/*
* Copyright (c) 2021, Tim Flynn <trflynn89@serenityos.org>
* Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -53,6 +54,7 @@ namespace SQL::AST {
__ENUMERATE_SQL_TOKEN("DEFERRED", Deferred, Keyword) \
__ENUMERATE_SQL_TOKEN("DELETE", Delete, Keyword) \
__ENUMERATE_SQL_TOKEN("DESC", Desc, Keyword) \
__ENUMERATE_SQL_TOKEN("DESCRIBE", Describe, Keyword) \
__ENUMERATE_SQL_TOKEN("DETACH", Detach, Keyword) \
__ENUMERATE_SQL_TOKEN("DISTINCT", Distinct, Keyword) \
__ENUMERATE_SQL_TOKEN("DO", Do, Keyword) \

1
Userland/Libraries/LibSQL/CMakeLists.txt
View file

@ -1,6 +1,7 @@
set(SOURCES
AST/CreateSchema.cpp
AST/CreateTable.cpp
AST/Describe.cpp
AST/Expression.cpp
AST/Insert.cpp
AST/Lexer.cpp

16
Userland/Libraries/LibSQL/Database.cpp
View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -47,6 +48,21 @@ ErrorOr<void> Database::open()
default_schema = SchemaDef::construct("default");
TRY(add_schema(*default_schema));
}
auto master_schema = TRY(get_schema("master"));
if (!master_schema) {
master_schema = SchemaDef::construct("master");
TRY(add_schema(*master_schema));
}
auto table_def = TRY(get_table("master", "internal_describe_table"));
if (!table_def) {
auto describe_internal_table = TableDef::construct(master_schema, "internal_describe_table");
describe_internal_table->append_column("Name", SQLType::Text);
describe_internal_table->append_column("Type", SQLType::Text);
TRY(add_table(*describe_internal_table));
}
return {};
}

1
Userland/Libraries/LibSQL/Database.h
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@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
* Copyright (c) 2021, Mahmoud Mandour <ma.mandourr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/

1
Userland/Libraries/LibSQL/SQLResult.h
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@ -19,6 +19,7 @@ namespace SQL {
#define ENUMERATE_SQL_COMMANDS(S) \
S(Create) \
S(Delete) \
S(Describe) \
S(Insert) \
S(Select) \
S(Update)