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Databases & SQL vocabulary · Indexes and Query Performance

Full table scan

Meaning in databases & SQL, with examples

nounCommon term

In databases & SQL, full table scan means: Reading every row of a table to find the ones a query needs, instead of jumping straight to them through an index.

In Turkish: tam tablo taraması

How it is used

Execution plans show it as 'Seq Scan' in PostgreSQL, 'type: ALL' in MySQL and 'Table Scan' or 'Clustered Index Scan' in SQL Server. On big tables it is a common cause of slow queries, but on small tables, or when most rows are needed anyway, it can actually be the fastest choice.

Example sentences

  1. Because the WHERE clause wraps the column in a function, the database does a full table scan.

  2. A full table scan on 200 rows is nothing to worry about.

Common collocations

  • do a full table scan
  • avoid a full table scan
  • sequential scan
  • table scan
  • 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.
  • 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.
  • slow queryA query that takes longer than an agreed limit to finish, slowing down the application and using up database resources.
  • query tuningThe work of making slow queries faster by studying their execution plans and then adding indexes, rewriting SQL or changing database settings.

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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