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Databases & SQL vocabulary · Indexes and Query Performance

Clustered index

Meaning in databases & SQL, with examples

nounAdvanced term

In databases & SQL, clustered index means: An index that decides the physical order in which a table's rows are stored, so a table can have only one; the other indexes are non-clustered.

In Turkish: kümelenmiş indeks, clustered index

How it is used

A key term in SQL Server, where the primary key becomes the clustered index by default, and in MySQL InnoDB, where the primary key is always the clustered index. PostgreSQL has no permanent clustered index; its CLUSTER command reorders a table only once.

Example sentences

  1. A random GUID as the clustered index causes page splits on every insert.

  2. The table has a clustered index on order_date and two non-clustered indexes.

Common collocations

  • clustered index
  • non-clustered index
  • clustered index scan
  • clustered index key
  • indexAn extra data structure built on one or more columns that lets the database find rows quickly without reading the whole table, like the index at the back of a book.
  • primary keyA column, or a set of columns, whose value uniquely identifies each row in a table. It cannot be empty and no two rows can share it.
  • full table scanReading every row of a table to find the ones a query needs, instead of jumping straight to them through an index.
  • execution planThe step-by-step strategy the database chooses to run a query, showing which indexes it uses, how tables are joined and how many rows it expects.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Indexes and Query Performance

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