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Query extension metadata and server state using the standard SQL interfaces below.

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System Views

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INFORMATION_SCHEMA.EXTENSIONS

Lists all currently installed VillageSQL extensions.
INSTALL EXTENSION and UNINSTALL EXTENSION are VillageSQL SQL extensions. They are not part of standard MySQL 8.4 syntax.
Known columns:
ColumnTypeDescription
EXTENSION_NAMEvarcharName of the installed extension
EXTENSION_VERSIONvarcharVersion string reported by the extension
Example: 
-- Install an extension (VillageSQL-specific syntax)
INSTALL EXTENSION vsql_complex;

-- List all installed extensions
SELECT * FROM INFORMATION_SCHEMA.EXTENSIONS;

-- Check a specific extension's version
SELECT EXTENSION_VERSION
FROM INFORMATION_SCHEMA.EXTENSIONS
WHERE EXTENSION_NAME = 'vsql_complex';
Illustrative output (actual version strings depend on installed extensions): 
+------------------+-------------------+
| EXTENSION_NAME   | EXTENSION_VERSION |
+------------------+-------------------+
| vsql_complex     | 0.0.1             |
| vsql_uuid        | 0.2.1             |
+------------------+-------------------+
EXTENSION_NAME values are lowercase, matching the name passed to make_extension(). The view reflects the current installed state.

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INFORMATION_SCHEMA.COLUMNS (Custom Types)

Columns using custom extension types are visible through the standard INFORMATION_SCHEMA.COLUMNS view. Custom types appear as extension_name.type_name in the DATA_TYPE and COLUMN_TYPE columns (e.g., vsql_complex.COMPLEX). Example: 
-- Find all columns using custom extension types
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE '%.%'
ORDER BY TABLE_SCHEMA, TABLE_NAME;

-- Find columns using a specific extension's types
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE 'vsql_complex.%';
Sample Output: 
+--------------+------------+-------------+---------------------+
| TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | DATA_TYPE           |
+--------------+------------+-------------+---------------------+
| mydb         | signals    | impedance   | vsql_complex.COMPLEX|
| mydb         | signals    | frequency   | vsql_complex.COMPLEX|
+--------------+------------+-------------+---------------------+

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Common Queries

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Find Extension Dependencies

Find which columns use a specific extension’s types before uninstalling: 
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE 'vsql_complex.%';

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List All Extensions and Their Custom Type Columns

-- All installed extensions
SELECT EXTENSION_NAME, EXTENSION_VERSION
FROM INFORMATION_SCHEMA.EXTENSIONS
ORDER BY EXTENSION_NAME;

-- All columns using custom types across all extensions
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE '%.%'
ORDER BY DATA_TYPE, TABLE_SCHEMA, TABLE_NAME;

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Find Tables Using Extension Types

SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE 'vsql_complex.%'
ORDER BY TABLE_SCHEMA, TABLE_NAME;

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System Variables

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veb_dir

Read-only at runtime. Path to the directory where the server looks for .veb extension bundle files. Set in my.cnf under [mysqld]; cannot be changed without a server restart. 
SHOW VARIABLES LIKE 'veb_dir';
Scope: Global, read-only at runtime. Configure in my.cnf: 
[mysqld]
veb_dir=/path/to/extensions/
Only a single directory is supported. See Managing Extensions for placement and troubleshooting.

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villagesql_server_version

Read-only global variable. Returns the VillageSQL version string compiled into the server binary. This is distinct from villagesql_schema_version, which tracks the internal metadata catalog version. 
SELECT @@villagesql_server_version;
-- Example output: 0.0.3

-- Show all VillageSQL system variables at once
SHOW VARIABLES LIKE 'villagesql_%';
Scope: Global, read-only. Cannot be set at runtime.

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Next Steps

Managing Extensions

Monitor and troubleshoot extensions

Install Extensions

Add new extensions

Extension Architecture

Understand the internals

Available Extensions

Browse extension catalog