Select (SQL): Difference between revisions

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A query includes a list of columns to include in the final result, normally immediately following the <code>SELECT</code> keyword. An asterisk ("<code>*</code>") can be used to specify that the query should return all columns of all the queried tables. <code>SELECT</code> is the most complex statement in SQL, with optional keywords and clauses that include:

* The <code>[[From (SQL)|FROM]]</code> clause, which indicates the table(s)tables to retrieve data from. The <code>FROM</code> clause can include optional <code>[[Join (SQL)|JOIN]]</code> subclauses to specify the rules for joining tables.

* The <code>[[Where (SQL)|WHERE]]</code> clause includes a comparison predicate, which restricts the rows returned by the query. The <code>WHERE</code> clause eliminates all rows from the result set where the comparison predicate does not evaluate to True.

* The <code>GROUP BY</code> clause projects rows having common values into a smaller set of rows. <code>GROUP BY</code> is often used in conjunction with SQL aggregation functions or to eliminate duplicate rows from a result set. The <code>WHERE</code> clause is applied before the <code>GROUP BY</code> clause.

* The <code>[[Having (SQL)|HAVING]]</code> clause includes a predicate used to filter rows resulting from the <code>GROUP BY</code> clause. Because it acts on the results of the <code>GROUP BY</code> clause, aggregation functions can be used in the <code>HAVING</code> clause predicate.

* The <code>[[Order by (SQL)|ORDER BY]]</code> clause identifies which column[s]columns to use to sort the resulting data, and in which direction to sort them (ascending or descending). Without an <code>ORDER BY</code> clause, the order of rows returned by an SQL query is undefined.

* The <code>DISTINCT</code> keyword<ref>

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