SQL SELECT: Difference between revisions

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=Overview=
=Overview=
A query consists in at least one (<code>[[#SELECT|SELECT]]</code>) and at most six categories of [[#Clauses|clauses]]
A query consists in at least one (<code>[[#SELECT|SELECT]]</code>) and at most six categories of [[#Clauses|clauses]]:
<font>
<font>
  [[#SELECT|SELECT]] FROM WHERE GROUP BY HAVING ORDER BY  
  [[#SELECT|SELECT]] FROM WHERE GROUP BY HAVING ORDER BY  
</font>
</font>


<syntaxhighlight lang='sql'>
SELECT;
</syntaxhighlight>
is a valid query, returns one empty row.


Upon execution, an SQL query returns a [[SQL#Result_Set|result set]].
Upon execution, an SQL query returns a [[SQL#Result_Set|result set]].


Query execution. SQL optimizer. Subqueries.





Revision as of 23:11, 22 May 2024

Internal

Overview

A query consists in at least one (SELECT) and at most six categories of clauses:

SELECT FROM WHERE GROUP BY HAVING ORDER BY 

SELECT;

is a valid query, returns one empty row.

Upon execution, an SQL query returns a result set.


Select all (possibly across multiple tables) then filter and discard with where.

Example

SELECT id, name FROM person WHERE id = 1;

Clauses

SELECT

FROM

FROM permanent|derived|temporary|virtual(view)

Table alias.

Querying Multiple Tables

Querying Multiple Tables

WHERE

The WHERE Clause

GROUP BY ... HAVING

(make sure I understand thoroughly and link)

ORDER BY

Subqueries