Commands and Statements Commands and Statements

Command SELECT - SQL FROM Clause Foundation

Specifies the tables and join conditions for an SQL SELECT command.

Syntax
   FROM <cTableName> [AS <cAliasName>]
   | FROM (<Expression>) [AS <cAliasName>]
   | FROM (<SubSelectExpression>) [AS <cAliasName>]
   | FROM JoinType JOIN <cTableName> JoinCondition [AS <cAliasName>]
   JoinType:
   INNER 
   | LEFT [OUTER] 
   | RIGHT [OUTER]
   | FULL [OUTER] 
   JoinCondition:
   ON <JoinExpression> 
   | USING <cFieldName> [, <cFieldName>] ]
Parameters
FROM <cTableName>
TBD
FROM <Expression>
TBD
FROM <SubSelectExpression>
<SubSelectExpression> specifies an SQL SELECT statement whose result set is used as an input for the query. Any type of SQL SELECT statement can be used with this parameter, including statements using joins and filters. However, the INTO and EVAL clauses can not be used in subselects.
INNER JOIN
INNER JOIN specifies that the query result contains the rows that match the join condition from both tables involved in the join. INNER JOINs are the most common type of join.
LEFT [OUTER] JOIN
In a LEFT [OUTER] JOIN the query result contains all rows of the element (table) specified on the left side of the JOIN keyword, but only the rows that match the join condition from the element located on the right of the join. The OUTER keyword is optional and has no effect other than to indicate that an outer join is created with the LEFT JOIN keywords.
RIGHT [OUTER] JOIN
RIGHT [OUTER] JOIN specifies that the query result contains all rows of the element (table) specified on the right side of the JOIN keyword, but only the rows that match the join condition from the element located on the left of the join. The OUTER keyword is optional and has no effect other than to indicate that an outer join is created with the RIGHT JOIN keywords.
FULL [OUTER] JOIN
FULL [OUTER] JOIN specifies that the query result contains all rows from both elements (tables) involved in the join, regardless of whether the rows match the join condition. The OUTER keyword is optional and has no effect other than to indicate that an outer join is created with the FULL JOIN keywords.
ON <JoinCondition>
ON <JoinCondition> specifies the conditions for joining the tables specified in the JOIN clause. Which rows from which table must meet these conditions, if at all, depends on the type of join being created.
Description

The FROM clause specifies one or more source elements of an SQL SELECT command. In most cases, the <cTableName> syntax is used which specifies the name of a table to be used as an input for the query. However, the results returned by expressions and subselects can also be used as the input for an SQL SELECT. In all cases, an alias name can be specified for the respective source element. Defining an alias allows for unambiguous and easy addressing of the respective element in the SQL SELECT statement, for example, in the column specification.

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