Select (SQL): Difference between revisions

Revision as of 13:36, 24 August 2023

Revision as of 03:22, 19 October 2023

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* <code>SELECT</code> clause is the list of [[column (database)|columns]] or SQL expressions that must be returned by the query. This is approximately the [[relational algebra]] [[Projection_(relational_algebra)|projection]] operation.

* <code>[[Alias (SQL)|AS]]</code> optionally provides an alias for each column or expression in the <code>SELECT</code> clause. This is the relational algebra [[Rename_(relational_algebra)|rename]] operation.

* <code>[[From (SQL)|FROM]]</code> specifies from which table to get the data.<ref>Omitting FROM clause isn'tis not standard, but allowed by most major DBMSes.</ref>

* <code>[[Where (SQL)|WHERE]]</code> specifies which rows to retrieve. This is approximately the relational algebra [[Selection_(relational_algebra)|selection]] operation.

* <code>[[Group by (SQL)|GROUP BY]]</code> groups rows sharing a property so that an [[aggregate function]] can be applied to each group.