SCHEMA_ID (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
Returns the schema ID associated with a schema name.
Database schemas act as namespaces or containers for objects, such as tables, views, procedures, and functions, that can be found in the sys.objects catalog view.
Each schema has an owner. The owner is a security principal.
Transact-SQL syntax conventions
Syntax
SCHEMA_ID ( [ schema_name ] )
Arguments
schema_name
The name of the schema. schema_name is sysname. If schema_name isn't specified, SCHEMA_ID returns the ID of the default schema of the caller.
Return types
int
NULL is returned if schema_name isn't a valid schema.
Remarks
SCHEMA_ID returns IDs of system schemas and user-defined schemas. SCHEMA_ID can be called in a select list, in a WHERE clause, and anywhere an expression is allowed.
Examples
A. Return the default schema ID of a caller
SELECT SCHEMA_ID();
B. Return the schema ID of a named schema
SELECT SCHEMA_ID('dbo');