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User-defined schemas within Synapse SQL

  • Artikkeli

In the sections below, you'll find various tips for using T-SQL user-defined schemas to develop solutions within Synapse SQL.

Schemas for application boundaries

Traditional analytics architecture often uses separate databases to create application boundaries based on workload, domain, or security. For example, a traditional SQL Server analytics infrastructure might include a staging database, an analytics database, and data mart databases. In this topology, each database operates as a workload and security boundary in the architecture.

Instead, Synapse SQL runs the entire analytics workload within one database. Cross database joins aren't permitted. Synapse SQL expects all tables used by the warehouse to be stored within the one database.

Note

Dedicated SQL pools do not support cross database queries of any kind. Consequently, analytics implementations that leverage this pattern will need to be revised. Serverless SQL pool supports cross database queries.

User-defined schema recommendations

Included are recommendations for consolidating workloads, security, domain, and functional boundaries by using user-defined schemas:

  • Use one database to run your entire analytics workload.
  • Consolidate your existing analytics environment to use one database.
  • Leverage user-defined schemas to provide the boundary previously implemented using databases.

If user-defined schemas haven't been used previously, then you have a clean slate. Use the old database name as the basis for your user-defined schemas in the Synapse SQL database.

If schemas have already been used, then you have a few options:

  • Remove the legacy schema names and start fresh
  • Keep the legacy schema names by pre-pending the legacy schema name to the table name
  • Retain the legacy schema names by implementing views over the table in an extra schema, which re-creates the old schema structure.

Note

On first inspection, option 3 may seem like the most appealing choice. Views are read only in Synapse SQL. Any data or table modification would need to be performed against the base table. Option 3 also introduces a layer of views into your system. You might want to give this some additional thought if you are already using views in your architecture.

Examples

Implement user-defined schemas based on database names.

CREATE SCHEMA [stg]; -- stg previously database name for staging database
GO
CREATE SCHEMA [edw]; -- edw previously database name for the analytics
GO
CREATE TABLE [stg].[customer] -- create staging tables in the stg schema
(       CustKey BIGINT NOT NULL
,       ...
);
GO
CREATE TABLE [edw].[customer] -- create analytics tables in the edw schema
(       CustKey BIGINT NOT NULL
,       ...
);

Keep the legacy schema names by pre-pending them to the table name. Use schemas for the workload boundary.

CREATE SCHEMA [stg]; -- stg defines the staging boundary
GO
CREATE SCHEMA [edw]; -- edw defines the analytics boundary
GO
CREATE TABLE [stg].[dim_customer] --pre-pend the old schema name to the table and create in the staging boundary
(       CustKey BIGINT NOT NULL
,       ...
);
GO
CREATE TABLE [edw].[dim_customer] --pre-pend the old schema name to the table and create in the analytics boundary
(       CustKey BIGINT NOT NULL
,       ...
);

Retain the legacy schema names using views.

CREATE SCHEMA [stg]; -- stg defines the staging boundary
GO
CREATE SCHEMA [edw]; -- stg defines the analytics boundary
GO
CREATE SCHEMA [dim]; -- edw defines the legacy schema name boundary
GO
CREATE TABLE [stg].[customer] -- create the base staging tables in the staging boundary
(       CustKey    BIGINT NOT NULL
,       ...
)
GO
CREATE TABLE [edw].[customer] -- create the base analytics tables in the analytics boundary
(       CustKey    BIGINT NOT NULL
,       ...
)
GO
CREATE VIEW [dim].[customer] -- create a view in the legacy schema name boundary for presentation consistency purposes only
AS
SELECT  CustKey
,       ...
FROM    [edw].customer
;

Note

Any change in schema strategy requires a review of the security model for the database. In many cases, you might be able to simplify the security model by assigning permissions at the schema level.

If more granular permissions are required, you can use database roles. For more information about database roles, see the Manage database roles and users article.

Next steps

For more development tips, see Synapse SQL development overview.