Interface Schema

All Known Subinterfaces:
SchemaPlus, SemiMutableSchema
All Known Implementing Classes:
AbstractSchema, CassandraSchema, CloneSchema, CsvSchema, DelegatingSchema, DruidSchema, ElasticsearchSchema, GeodeSchema, GeodeSimpleSchema, JdbcCatalogSchema, JdbcSchema, MongoSchema, PigSchema, ReflectiveSchema, SplunkSchema, TpcdsSchema, TpchSchema

public interface Schema
A namespace for tables and functions.

A schema can also contain sub-schemas, to any level of nesting. Most providers have a limited number of levels; for example, most JDBC databases have either one level ("schemas") or two levels ("database" and "catalog").

There may be multiple overloaded functions with the same name but different numbers or types of parameters. For this reason, getFunctions(java.lang.String) returns a list of all members with the same name. Calcite will call Schemas.resolve(org.apache.calcite.rel.type.RelDataTypeFactory, String, java.util.Collection, java.util.List) to choose the appropriate one.

The most common and important type of member is the one with no arguments and a result type that is a collection of records. This is called a relation. It is equivalent to a table in a relational database.

For example, the query

select * from sales.emps

is valid if "sales" is a registered schema and "emps" is a member with zero parameters and a result type of Collection(Record(int: "empno", String: "name")).

A schema may be nested within another schema; see getSubSchema(String).

  • Method Details

    • getTable

      Table getTable​(String name)
      Returns a table with a given name, or null if not found.
      Parameters:
      name - Table name
      Returns:
      Table, or null
    • getTableNames

      Set<String> getTableNames()
      Returns the names of the tables in this schema.
      Returns:
      Names of the tables in this schema
    • getType

      RelProtoDataType getType​(String name)
      Returns a type with a given name, or null if not found.
      Parameters:
      name - Table name
      Returns:
      Table, or null
    • getTypeNames

      Set<String> getTypeNames()
      Returns the names of the types in this schema.
      Returns:
      Names of the tables in this schema
    • getFunctions

      Collection<Function> getFunctions​(String name)
      Returns a list of functions in this schema with the given name, or an empty list if there is no such function.
      Parameters:
      name - Name of function
      Returns:
      List of functions with given name, or empty list
    • getFunctionNames

      Set<String> getFunctionNames()
      Returns the names of the functions in this schema.
      Returns:
      Names of the functions in this schema
    • getSubSchema

      Schema getSubSchema​(String name)
      Returns a sub-schema with a given name, or null.
      Parameters:
      name - Sub-schema name
      Returns:
      Sub-schema with a given name, or null
    • getSubSchemaNames

      Set<String> getSubSchemaNames()
      Returns the names of this schema's child schemas.
      Returns:
      Names of this schema's child schemas
    • getExpression

      Expression getExpression​(SchemaPlus parentSchema, String name)
      Returns the expression by which this schema can be referenced in generated code.
      Parameters:
      parentSchema - Parent schema
      name - Name of this schema
      Returns:
      Expression by which this schema can be referenced in generated code
    • isMutable

      boolean isMutable()
      Returns whether the user is allowed to create new tables, functions and sub-schemas in this schema, in addition to those returned automatically by methods such as getTable(String).

      Even if this method returns true, the maps are not modified. Calcite stores the defined objects in a wrapper object.

      Returns:
      Whether the user is allowed to create new tables, functions and sub-schemas in this schema
    • snapshot

      Schema snapshot​(SchemaVersion version)
      Returns the snapshot of this schema as of the specified time. The contents of the schema snapshot should not change over time.
      Parameters:
      version - The current schema version
      Returns:
      the schema snapshot.