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Select (SQL)
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<p>The <a href="/facts/SQL/UjQLJcYm">SQL</a> SELECT statement returns a <a href="/facts/Result_set/G5nUHQbv">result set</a> of rows, from one or more <a href="/facts/Table_(database)/5INvK1Vd">tables</a>. </p><p>A SELECT statement retrieves zero or more rows from one or more <a href="/facts/Database_Tables/5INvK1Vd">database tables</a> or database <a href="/facts/View_(database)/6B00yj6A">views</a>. In most applications, SELECT is the most commonly used <a href="/facts/Data_manipulation_language/eeJRDUEl">data manipulation language</a> (DML) command. As SQL is a <a href="/facts/Declarative_programming/gogtdzcJ">declarative programming</a> language, SELECT queries specify a result set, but do not specify how to calculate it. The database translates the query into a "<a href="/facts/Query_plan/VDsyMQFE">query plan</a>" which may vary between executions, database versions and database software. This functionality is called the "<a href="/facts/Query_optimizer/KsSwxtw8">query optimizer</a>" as it is responsible for finding the best possible execution plan for the query, within applicable constraints. </p><p>The SELECT statement has many optional clauses: </p> <ul><li>SELECT list is the list of <a href="/facts/Column_(database)/WB91xSVs">columns</a> or SQL expressions to be returned by the query. This is approximately the <a href="/facts/Relational_algebra/7tjTFXdf">relational algebra</a> <a href="/facts/Projection_(relational_algebra)/YgQm2wgA">projection</a> operation.</li> <li><a href="/facts/Alias_(SQL)/EUpmKC9y">AS</a> optionally provides an alias for each column or expression in the SELECT list. This is the relational algebra <a href="/facts/Rename_(relational_algebra)/s4D5PM4v">rename</a> operation.</li> <li><a href="/facts/From_(SQL)/xLyuQAo8">FROM</a> specifies from which table to get the data.</li> <li>WHERE specifies which rows to retrieve. This is approximately the relational algebra <a href="/facts/Selection_(relational_algebra)/vHT4UCT1">selection</a> operation.</li> <li><a href="/facts/Group_by_(SQL)/lJ3oRhv2">GROUP BY</a> groups rows sharing a property so that an <a href="/facts/Aggregate_function/685obrqz">aggregate function</a> can be applied to each group.</li> <li><a href="/facts/Having_(SQL)/V62LRz0m">HAVING</a> selects among the groups defined by the GROUP BY clause.</li> <li><a href="/facts/Order_by_(SQL)/TbJcMN1x">ORDER BY</a> specifies how to order the returned rows.</li></ul>