This topic describes the terms that are used in ApsaraDB for SelectDB to help you better understand ApsaraDB for SelectDB.
region
A region indicates the geographical location at which ApsaraDB for SelectDB resources reside. You must specify a region when you purchase ApsaraDB for SelectDB resources. You cannot change the region after the resources are created.
zone
A zone indicates the physical area that has an independent power supply and an independent network in a region. Zones are isolated from each other and can communicate with each other over an internal network in the same region. The network latency between instances within the same zone is lower than that in different zones.
instance
ApsaraDB for SelectDB instances provide computing, storage, and network resources. Resources are isolated between instances.
cluster
Clusters in an ApsaraDB for SelectDB instance support a compute-storage separation architecture. Multiple compute clusters share stored data in an instance. ApsaraDB for SelectDB clusters provide computing resources, such as vCPUs and memory, and cache resources. Computing capacity is isolated between clusters to meet your requirements of performance and usage duration for different services.
ApsaraDB for SelectDB storage
ApsaraDB for SelectDB uses a compute-storage separation architecture and allows multiple compute clusters to share stored data in an instance, which effectively reduces the number of replicas. In addition, ApsaraDB for SelectDB works with Object Storage Service (OSS) to significantly reduce storage costs.
catalog
A catalog is a collection of databases. Catalogs are divided into the internal catalog and external catalogs. The internal catalog contains the internal databases of ApsaraDB for SelectDB. External catalogs can be connected to data sources such as Hive, Iceberg, and Hudi and used for queries.
database
A database belongs to a catalog. A database contains tables, columns, views, functions, and data types.
table
A table belongs to a database. In ApsaraDB for SelectDB, tables are used to store structured data. A table consists of rows and columns. Each row indicates a row of data. Each column indicates a field in a row of data.
ApsaraDB for SelectDB supports the following data models:
Aggregate key model
Unique key model
Duplicate key model
index
An index is a structure that sorts the values of one or more columns in a table. You can use indexes to filter data in tables and accelerate queries. ApsaraDB for SelectDB supports the following indexes:
Built-in intelligent indexes, including zone map indexes and prefix indexes.
Custom secondary indexes, including inverted indexes, bitmap indexes, and Bloom filter indexes.
view
A view is a virtual table that is derived from one or more base tables or views. ApsaraDB for SelectDB automatically maintains the data of materialized views. This ensures data consistency between a base table and a materialized view when data is imported or deleted. You are not charged additional fees for maintaining data. When you query data, the system automatically matches an optimal materialized view and reads data from the materialized view.
function
Functions can be used to query, collect statistics on, and calculate data stored in databases. Functions can be used with SQL statements or as custom SQL functions. Common functions are divided into the following types:
Aggregate functions
Aggregate functions are used to calculate the values of a dataset and return the aggregated value. Common aggregate functions include SUM, AVG, COUNT, MAX, and MIN. In most cases, aggregate functions are used to collect statistics and calculate data.
String functions
String functions are used to process strings, such as appending strings, truncating strings, replacing strings, and converting the uppercase letters in a string to lowercase letters. Common string functions include SUBSTRING, CONCAT, REPLACE, UPPER, and LOWER.
Mathematical functions
Mathematical functions are used to calculate numbers. Common mathematical functions include ABS, CEIL, FLOOR, and ROUND.
Date and time functions
Date and time functions are used to process data of the date or time type, such as formatting data of the date or time type, calculating data of the date or time type, and adding or subtracting data of the date or time type. Common date and time functions include NOW, DATE_FORMAT, DATEDIFF, and DATE_ADD.
Conditional functions
Conditional functions return different results based on conditions, such as IF and CASE.