ESQL IBM PDF

You can improve message flow performance with ESQL by using some optimization techniques. When you write your ESQL code, you can use several techniques to improve the performance of your message flows. The following sections contain guidance about how to improve the performance of your ESQL code:. Array subscripts [ ] are expensive in terms of performance because of the way in which subscript is evaluated dynamically at run time. By avoiding the use of array subscripts wherever possible, you can improve the performance of your ESQL code. You can use reference variables instead, which maintain a pointer into the array and which can then be reused; for example:.

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You can use ESQL statements to manipulate message trees, update databases, or interact with nodes. The following table summarizes the ESQL statements and what they do. IF statement Processes a set of statements based on the result of evaluating condition expressions. LOOP statement Processes a sequence of statements repeatedly and unconditionally. If the expression evaluates to TRUE, executes the statements again.

SET statement Evaluates a source expression, and assigns the result to the target entity. Message tree manipulation statements: ATTACH statement Attaches a portion of a message tree into a new position in the message hierarchy. FOR statement Iterates through a list for example, a message array. MOVE statement Changes the field pointed to by a target reference variable. LOG statement Writes a record to the event or user trace log.

This is used by an error handler, when it cannot handle an exception, to give an error handler in higher scope the opportunity of handling the exception. END statement. CALL statement. CASE statement. Uses rules defined in WHEN clauses to select a block of statements to execute. Declares one or more variables that can be used to store temporary values. IF statement. Processes a set of statements based on the result of evaluating condition expressions.

LEAVE statement. LOOP statement. Processes a sequence of statements, then evaluates a condition expression. Stops processing the current function or procedure and passes control back to the caller. SET statement. Evaluates a source expression, and assigns the result to the target entity.

THROW statement. WHILE statement. Evaluates a condition expression, and if it is TRUE executes a sequence of statements. Attaches a portion of a message tree into a new position in the message hierarchy. Detaches and destroys a portion of a message tree, allowing its memory to be reused. FOR statement. MOVE statement. Deletes rows from a table in an external database based on a search condition. Takes a character value and passes it as an SQL statement to an external database.

Updates the values of specified rows and columns in a table in an external database. This statement is optional and is used in an ESQL file to explicitly identify the schema that contains the file.

EVAL statement. Takes a character value, interprets it as an SQL statement, and executes it. LOG statement. Re-throws the current exception if any.

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Developing ESQL

When you create a message flow, you include input nodes that receive the messages and, optionally, output nodes that send out new or updated messages. If required by the processing that must be performed on the message, you can include other nodes after the input node that complete the actions that your applications need. Some of the built-in nodes enable you to customize the processing that they provide. The Compute , Database , DatabaseInput , and Filter nodes require you to provide a minimum level of ESQL, and you can provide much more than the minimum to control precisely the behavior of each node. This set of topics discusses ESQL and the ways in which you can use it to customize these nodes. You can use the Mapping node to customize the processing visually. For more information, see Using message maps.

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ESQL statements

When you create a message flow, you include input nodes that receive the messages and, optionally, output nodes that send out new or updated messages. If required by the processing that must be performed on the message, you can include other nodes after the input node that complete the actions that your applications need. Some of the built-in nodes enable you to customize the processing that they provide. The Compute , Database , DatabaseInput , and Filter nodes require you to provide a minimum level of ESQL, and you can provide much more than the minimum to control precisely the behavior of each node. This set of topics discusses ESQL and the ways in which you can use it to customize these nodes. You can use the Mapping node to customize the processing visually.

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ESQL string manipulation functions

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