Stewart Smith: Drizzle metadata tables
Giuseppe has a great post about the Evolution of MySQL metadata, and I thought I’d have a look at what we have in Drizzle. It’s pretty easy to work out how many tables are in each schema, we just query the standard INFORMATION_SCHEMA.TABLES view:
drizzle> select table_schema,count(table_name)
-> from information_schema.tables
-> group by table_schema;
+--------------------+-------------------+
| table_schema | count(table_name) |
+--------------------+-------------------+
| DATA_DICTIONARY | 53 |
| INFORMATION_SCHEMA | 20 |
+--------------------+-------------------+
2 rows in set (0 sec)
In Drizzle it’s important to note that there is a differentiation between SQL Standard INFORMATION_SCHEMA tables (found in the INFORMATION_SCHEMA schema) and the extensions and extra information available from Drizzle that is Drizzle specific (found in DATA_DICTIONARY). Since I know that the PostgreSQL version I have on my laptop (8.4) also implements INFORMATION_SCHEMA, I can run this query there as well:
stewart=# select table_schema,count(table_name)
from information_schema.tables
group by table_schema;
table_schema | count
--------------------+-------
information_schema | 55
pg_catalog | 78
(2 rows)
If we had written the query to the Drizzle DATA_DICTIONARY tables, it only may have been portable – and as we can see, certainly wouldn’t have run unmodified on PostgreSQL. Personally, I really like this feature, and wish more systems did something like it.
URL: http://www.flamingspork.com/blog/2011/02/08/drizzle-metadata-tables/
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