In SESAM/SQL, query expressions are the most important means of querying data.
This chapter describes the syntax of query expressions and provides you with an explanation of the various joins. It is subdivided into the following sections:
Table specifications
SELECT expression
Table queries
Joins
Subquery
Combining query expressions with UNION
Combining query expressions with EXCEPT DISTINCT
Updatability of query expressions
Overview
You use query expressions to select rows and columns from base tables and views. The rows found constitute the derived table.
A query expression is part of an SQL statement. A query expression can occur in subqueries or in any of the following SQL statements:
CREATE VIEW DECLARE CURSOR INSERT | Define a view Declare a cursor Insert rows in table |
The examples in this chapter only show the relevant query expression. Without the associated subquery or SQL statement, the examples are of course not executable.
If you want to use a subquery in an SQL statement, you must own the table referenced in the subquery or have SELECT privilege for the table involved.
query_expression ::= [ query_expression { UNION [ALL | DISTINCT] | EXCEPT [DISTINCT] }]
{ select_expression | TABLE table | join_expression | ( query_expression ) }
select_expression
SELECT expression (see section "SELECT expression")
TABLE table
Table query, see section "TABLE - Table query".
join_expression
Join expression (see section "Join expression")
(query_expression)
Subquery, see section "Subquery".
UNION
Combine two query expressions with UNION, see section "Combining query expressions with UNION".
EXCEPT DISTINCT
Combine two query expressions with EXCEPT, see section "Combining query expressions with EXCEPT".