Specifying FOR READ ONLY in the cursor declaration, or including a FOR READ ONLY clause in the statement, renders the statement read-only. In other words, a FOR READ ONLY clause, or the appropriate read-only cursor declaration when using a client API, overrides any other updatability specification.

If the outermost block of a SELECT statement contains an ORDER BY clause, and the statement does not specify FOR UPDATE, then the cursor is read-only. If the SQL SELECT statement specifies FOR XML, then the cursor is read-only. Otherwise, the cursor is updatable.

For updatable statements, SQL Anywhere provides both optimistic and pessimistic concurrency control mechanisms on cursors to ensure that a result set remains consistent during scrolling operations. These mechanisms are alternatives to using INSENSITIVE cursors or snapshot isolation, although they have different semantics and tradeoffs.

The specification of FOR UPDATE can affect whether a cursor is updatable. However, in SQL Anywhere, the FOR UPDATE syntax has no other effect on concurrency control. If FOR UPDATE is specified with additional parameters, SQL Anywhere alters the processing of the statement to incorporate one of two concurrency control options as follows:

Pessimistic or optimistic concurrency is specified at the cursor level either through options with DECLARE CURSOR or FOR statements, or though the concurrency setting API for a specific programming interface. If a statement is updatable and the cursor does not specify a concurrency control mechanism, the statement's specification is used. The syntax is as follows:

FOR UPDATE ( column-list ) enforces the restriction that only named result set attributes can be modified in a subsequent UPDATE WHERE CURRENT OF statement.

• DECLARE statement
• FOR statement