WL#2073: Schemas in ANSI style
Affects: Server-7.1 — Status: Un-Assigned — Priority: Very High
Given that we will map databases to schemas (as in WL#2071 Database = Schema), our next step is to support all ANSI/ISO "schema" statements and capabilities. Most of the description of this task was salvaged from WL#942 progress reports. Originally WL#942 was "Database = schema", but as it slowly became a "Catalogs" task the original requirement was destroyed. Despite my efforts to recover all the original, the text is now quite a mess. A MySQL "database" is analogous to a standard-SQL "schema". Given that decision, we can do some mapping. There will be a full hierarchy "catalog.schema.table" but it is equivalent to "catalog.database.table" and not "database.schema.table". The catalog level does not need to be implemented immediately: catalogs are a non-core feature, not required for the NIST tests, and not used in all DBMSs. But there is a separate worklog task for catalogs now, WL#942. When the catalog level is implemented, this means that the OS directory structure must change. The top level is catalog, within that are the schema directories. We did not discuss whether InnoDB would need any change. The catalog directory does not have to "include" the schema directories. As long as there is a way to "point to" the schema directories from the catalog directory, and vice versa, the DBMS can know what the hierarchy is. This might make a transition easier. Connector/J and MyODBC shall both return "schema" instead of "catalog" for the functions that ask what the equivalent name is for "database". These statements are equivalent: USE DATABASE = SET SCHEMA DROP DATABASE = DROP SCHEMA CREATE DATABASE = CREATE SCHEMA Monty has also suggested that we could add support for these statements, presumably to make transition easier: USE CATALOG catalog_name; USE SCHEMA|DATABASE schema_name; USE catalog_name.schema_name; The following details have not been agreed upon, but seem uncontroversial. There must be a "default catalog". In the present structure (which has no real 3-level hierarchy) the default catalog is always "SYSTEM", or "PUBLIC", or whatever. Every schema has an "owner". For us, this "owner" is the user who said "CREATE SCHEMA" or "CREATE DATABASE". For always-present databases like mysql or test, there is an arbitrary owner, which I'll again call "SYSTEM". In standard SQL it is illegal for any user to create a table in a schema that he/she does not own -- but we cannot follow standard SQL in that respect. Also, the "owner" of a schema has ALL PRIVILEGES on all tables in the schema automatically, even on the tables he/she did not create. (This may be undesirable, so it is a detail that's subject to change.). There is a schema INFORMATION_SCHEMA. It is virtual, that is, there is no directory structure of this name. The owner of INFORMATION_SCHEMA is a user named _SYSTEM (notice that this name is illegal in standard SQL, so that one cannot connect using this name). The description of INFORMATION_SCHEMA is in WL#173. A table is always within a schema. A character set or a collation is always within INFORMATION_SCHEMA. However, these objects are always the same in MySQL, so there is never a need to qualify them with INFORMATION_SCHEMA.latin1_general_ci or whatever. That should be legal, but isn't necessary. A user is NOT within a schema. One does not qualify a user name. In standard SQL, a user is not even within a catalog. It is a system-wide object. A privilege IS within a schema. The privilege is subsidiary to the object and not subsidiary to the user. Since we already store privilege information in the "user" database (i.e. the "user" SCHEMA), this might be okay. A procedure is always within a schema. In standard SQL, a built-in procedure (such as SUBSTRING) is in INFORMATION_SCHEMA, but I understand that we will not try to implement such a fiction. We have discussed the concept of a "public schema" or "public database". It could be named mysql. My preference would be a new one, named PUBLIC, which anyone can read, but only a limited number of users can write. Primarily we want this schema to store common-to-all procedures in. On startup, the public schema is the CURRENT schema. The CURRENT schema is usually not the same as the DEFAULT schema. The mechanism for changing the CURRENT schema is not yet known. The notation .table shall mean "<current schema name> . table". In other words, an empty space before a dot shall be interpreted as the current schema name. I suggested that we do not need a public or current schema, that we should use the standard-SQL PATH statement, but that motion did not pass. So a basic installation looks like this: ----------- -------- - catalog - - user - ----------- -------- | |________________________________ | | | ---------------- ----------- ------------------- - information_ - - public - - schemas created - - schema - - - - by users - ---------------- ----------- ------------------- | | | ----------------- ------------ ------------------- - metadata view - - common - - tables created - - or - - routines - - by users - - _system - ------------ ------------------- - object - ----------------- Remember that everything in information_schema is virtual, and we don't need a public schema until 5.0, so the above diagram doesn't really represent a drastic set of changes. Eventually we want to claim compliance with SQL standard feature F031 "Basic schema manipulation". We would also like to support SQL standard feature F311 "Schema definition statement" (core) We have to support "CREATE SCHEMA <schema name> + authorizations + object-creation". For example: CREATE SCHEMA S AUTHORIZATION PETER; CREATE SCHEMA S CREATE TABLE T (S1 INT); CREATE SCHEMA S ... CREATE TABLE T ... ... CREATE VIEW V ... ... GRANT ... ; The "AUTHORIZATION user-name" clause has no analogue in current MySQL, it should become the owner. The "CHARACTER SET character-set-name" clause (not illustrated) has an analogue in current MYSQL, it should become the database character set. The "CHARACTER SET character-set-name" clause (not illustrated) has an analogue in current MYSQL, it should become the database character set. These statements are equivalent: USE DATABASE = SET SCHEMA DROP DATABASE = DROP SCHEMA CREATE DATABASE = CREATE SCHEMA The full syntax for CREATE SCHEMA is in SQL-99 Complete, Really (pages 343ff). The only things I should add are: -- NIST assumes that CREATE SCHEMA implies SET SCHEMA, that is, CREATE DATABASE implies USE DATABASE. I don't see why. It's not certain that we'll allow this. Monty has also suggested that we could add support for these statements, presumably to make transition easier: USE CATALOG catalog_name; USE SCHEMA|DATABASE schema_name; USE catalog_name.schema_name; The following details have not been agreed upon, but seem uncontroversial. -- SQL:2003 allows SET COLLATION .. But we'll worry about that later. Additional note, we should look at following the complete spec for CREATE SCHEMA and allow all create tables that occur as a part of it to not test for foeign key attributes until the schema is loaded (aka this allows two tables that rely on each other to be loaded). This task is a requirement for SAP DB compatibility, Milestone2 "M2 Schemas". See also: WL#2071 "Database = Schema" Write specification for implementation of schemas in MySQL. Note: Done, Worklog entry #942. Add CREATE SCHEMA and DROP SCHEMA, as in SQL-99. Add the framework for an implicit schema, for cases where no CREATE SCHEMA statement has been executed. Map the AUTHORIZATION clause of the CREATE SCHEMA statement to the owner of all tables created for the schema. This will fulfill the requirement that SAP DB tables have owners. Note that this task is related to that of establishing standard security handling; MySQL must have the ability to create users and user groups before CREATE SCHEMA can define an owner. Modify the CREATE TABLE statement to allow the owner to be explicitly defined, i.e. CREATE TABLE <owner>.<name> and CREATE TABLE TEMP.<name>. Add a user (i.e. an owner) called TEMP, to specify a temporary table. Modify the CREATE TEMPORARY TABLE statement to support the creation of a temporary table with the syntax CREATE TABLE TEMP.<table name>. For each user, add a silent schema with the same name as the user name. SAP DB's qualification level is users/owners, while MySQL's is schemas. By making sure there is a one-to-one relationship between a schema and a user you can ensure that there will be no conflict. Feature requests: BUG#5754 Please: SCHEMA & GROUP support
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