In various SQL implementations, a hint is an addition to the SQL standard that instructs the

database engine A database engine (or storage engine) is the underlying software component that a database management system (DBMS) uses to create, read, update and delete (CRUD) data from a database. Most database management systems include their own application ...

on how to execute the query. For example, a hint may tell the engine to use or not to use an

index Index (or its plural form indices) may refer to: Arts, entertainment, and media Fictional entities * Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index'' * The Index, an item on a Halo megastru ...

(even if the

query optimizer Query optimization is a feature of many relational database management systems and other databases such as NoSQL and graph databases. The query optimizer attempts to determine the most efficient way to execute a given query by considering the pos ...

would decide otherwise).

Implementation

Different database engines use different approaches in implementing hints. *

MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database o ...

uses its own extension to the SQL standard, where a

table Table may refer to: * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (landform), a flat area of land * Table (information), a data arrangement with rows and columns * Table (database), how the table data ...

name may be followed by , or keywords. *

Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word '' ...

implements hints by using specially-crafted

comment Comment may refer to: * Comment (linguistics) or rheme, that which is said about the topic (theme) of a sentence * Bernard Comment (born 1960), Swiss writer and publisher Computing * Comment (computer programming), explanatory text or informa ...

s in the query that begin with a symbol, thus not affecting SQL compatibility. * EDB Postgres Advanced Server (a proprietary version of

PostgreSQL PostgreSQL (, ), also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to its origins as a successor to the In ...

from

EnterpriseDB EnterpriseDB (EDB), a privately held company based in Massachusetts, provides software and services based on the open-source database PostgreSQL (also known as Postgres), and is one of the largest contributors to Postgres. EDB develops and int ...

) offers hints compatible with those of Oracle. *

Microsoft SQL Server Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ma ...

offers hints via the keyword MSSQL 2017 Documentation
/ref>

References

SQL {{database-stub

Implementation

See also

References