Add DESCRIBE TABLE SQL command support

[hoangsonww]

This pull request introduces support for the standard SQL DESCRIBE (and DESC) command, allowing users to view column metadata for tables directly from the SQL workflow. The changes span parser, engine, and documentation updates to provide a seamless introspection experience.

SQL Introspection Feature:

• Added parsing support for DESCRIBE and DESC statements in the SQL parser, including a new DescribeTableQuery type and corresponding logic to extract the table name. (src/query/sql_parser.cpp, src/query/sql_parser.h) [1] [2] [3] [4]
• Updated the query execution engine to handle DESCRIBE_TABLE queries, returning detailed column metadata such as name, type, nullability, and default value. (src/engine/database_engine.cpp)
• Introduced a utility function to convert internal value types to human-readable SQL type strings for output formatting. (src/types/value.cpp, src/types/value.h) [1] [2]

User Experience Improvements:

• Enhanced CLI help output to include DESCRIBE [TABLE] as a supported command. (cli_main.cpp)
• Updated documentation to announce the new DESCRIBE feature and provide usage guidance for users. (README.md)

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Project	Deployment	Preview	Comments	Updated (UTC)
lattice-db-next-gen-dbms	Ready	Preview	Comment	Sep 26, 2025 11:46pm

[Copilot]

Pull Request Overview

This PR adds DESCRIBE TABLE SQL command support to enable schema introspection. It implements full parsing, execution, and documentation for the DESCRIBE/DESC commands to show table metadata.

• Adds new value_type_to_string helper function for consistent type formatting
• Implements DESCRIBE/DESC SQL parsing and execution with proper error handling
• Updates CLI help and README documentation to include the new functionality

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/types/value.h	Adds declaration for value_type_to_string helper function
src/types/value.cpp	Implements value_type_to_string with switch statement for all ValueType cases
src/query/sql_parser.h	Adds DESCRIBE_TABLE query type and DescribeTableQuery struct
src/query/sql_parser.cpp	Implements DESCRIBE/DESC parsing with optional TABLE keyword support
src/engine/database_engine.cpp	Implements DESCRIBE query execution returning formatted schema information
cli_main.cpp	Updates CLI help text to include DESCRIBE command
README.md	Documents new DESCRIBE functionality with usage notes

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[Copilot]

Pull Request Overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.

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[hoangsonww]

This pull request introduces support for the standard SQL DESCRIBE (or DESC) command, allowing users to view table schema metadata directly from the CLI. The implementation includes parser and engine changes, as well as user-facing documentation and CLI help updates.

SQL Introspection Feature:

• Added support for parsing and executing DESCRIBE table_name; and DESC table_name; commands, enabling users to inspect table columns, types, nullability, and default values. (src/query/sql_parser.cpp, src/query/sql_parser.h, src/engine/database_engine.cpp) [1] [2] [3] [4] [5] [6] [7]

• Implemented a helper function value_type_to_string to convert internal column types to human-readable strings for display in the DESCRIBE output. (src/types/value.cpp, src/types/value.h) [1] [2]

CLI and Documentation Updates:

• Updated CLI help output to include DESCRIBE [TABLE] as a supported command. (cli_main.cpp)
• Added a note to the README.md highlighting the new SQL introspection feature for user awareness. (README.md)