A schema adapter allows Calcite to read particular kind of data, presenting the data as tables within a schema.
Many projects and products use Apache Calcite for SQL parsing, query optimization, data virtualization/federation, and materialized view rewrite. Some of them are listed on the [“powered by Calcite”]({{ site.baseurl }}/docs/powered_by.html) page.
A driver allows you to connect to Calcite from your application.
The JDBC driver is powered by [Avatica]({{ site.avaticaBaseurl }}/docs/). Connections can be local or remote (JSON over HTTP or Protobuf over HTTP).
The basic form of the JDBC connect string is
jdbc:calcite:property=value;property2=value2
where property, property2 are properties as described below. (Connect strings are compliant with OLE DB Connect String syntax, as implemented by Avatica's ConnectStringParser.)
| Property | Description |
|---|---|
| approximateDecimal | Whether approximate results from aggregate functions on DECIMAL types are acceptable |
| approximateDistinctCount | Whether approximate results from COUNT(DISTINCT ...) aggregate functions are acceptable |
| approximateTopN | Whether approximate results from “Top N” queries * (ORDER BY aggFun() DESC LIMIT n) are acceptable |
| caseSensitive | Whether identifiers are matched case-sensitively. If not specified, value from lex is used. |
| conformance | SQL conformance level. Values: DEFAULT (the default, similar to PRAGMATIC_2003), ORACLE_10, ORACLE_12, PRAGMATIC_99, PRAGMATIC_2003, STRICT_92, STRICT_99, STRICT_2003, SQL_SERVER_2008. |
| createMaterializations | Whether Calcite should create materializations. Default false. |
| defaultNullCollation | How NULL values should be sorted if neither NULLS FIRST nor NULLS LAST are specified in a query. The default, HIGH, sorts NULL values the same as Oracle. |
| druidFetch | How many rows the Druid adapter should fetch at a time when executing SELECT queries. |
| forceDecorrelate | Whether the planner should try de-correlating as much as possible. Default true. |
| fun | Collection of built-in functions and operators. Valid values: “standard” (the default), “oracle”. |
| lex | Lexical policy. Values are ORACLE (default), MYSQL, MYSQL_ANSI, SQL_SERVER, JAVA. |
| materializationsEnabled | Whether Calcite should use materializations. Default false. |
| model | URI of the JSON model file. |
| parserFactory | Parser factory. The name of a class that implements SqlParserImplFactory and has a public default constructor or an INSTANCE constant. |
| quoting | How identifiers are quoted. Values are DOUBLE_QUOTE, BACK_QUOTE, BRACKET. If not specified, value from lex is used. |
| quotedCasing | How identifiers are stored if they are quoted. Values are UNCHANGED, TO_UPPER, TO_LOWER. If not specified, value from lex is used. |
| schema | Name of initial schema. |
| schemaFactory | Schema factory. The name of a class that implements SchemaFactory and has a public default constructor or an INSTANCE constant. Ignored if model is specified. |
| schemaType | Schema type. Value must be “MAP” (the default), “JDBC”, or “CUSTOM” (implicit if schemaFactory is specified). Ignored if model is specified. |
| spark | Specifies whether Spark should be used as the engine for processing that cannot be pushed to the source system. If false (the default), Calcite generates code that implements the Enumerable interface. |
| timeZone | Time zone, for example “gmt-3”. Default is the JVM's time zone. |
| typeSystem | Type system. The name of a class that implements RelDataTypeSystem and has a public default constructor or an INSTANCE constant. |
| unquotedCasing | How identifiers are stored if they are not quoted. Values are UNCHANGED, TO_UPPER, TO_LOWER. If not specified, value from lex is used. |
To make a connection to a single schema based on a built-in schema type, you don't need to specify a model. For example,
jdbc:calcite:schemaType=JDBC; schema.jdbcUser=SCOTT; schema.jdbcPassword=TIGER; schema.jdbcUrl=jdbc:hsqldb:res:foodmart
creates a connection with a schema mapped via the JDBC schema adapter to the foodmart database.
Similarly, you can connect to a single schema based on a user-defined schema adapter. For example,
jdbc:calcite:schemaFactory=org.apache.calcite.adapter.cassandra.CassandraSchemaFactory; schema.host=localhost; schema.keyspace=twissandra
makes a connection to the Cassandra adapter, equivalent to writing the following model file:
{% highlight json %} { “version”: “1.0”, “defaultSchema”: “foodmart”, “schemas”: [ { type: ‘custom’, name: ‘twissandra’, factory: ‘org.apache.calcite.adapter.cassandra.CassandraSchemaFactory’, operand: { host: ‘localhost’, keyspace: ‘twissandra’ } } ] } {% endhighlight %}
Note how each key in the operand section appears with a schema. prefix in the connect string.