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ABL Reference
ABL Syntax Reference : BUFFER-COMPARE statement


Performs a bulk comparison of two records (source and target) by comparing source and target fields of the same name for equality and storing the result in a field. You can specify a list of fields to exclude, or a list of fields to include. You can also specify WHEN...THEN phrases. For all such phrases you specify, the AVM evaluates the WHEN portion, and if it evaluates to TRUE, the AVM executes the THEN portion.


[ { EXCEPT | USING } field ... ] TO target
[ SAVE [ RESULT IN ] result-field ]
[ WHEN field compare-operator expression
THEN statement-or-block ] ...
The source database table, buffer, temp-table, or work table.
EXCEPT field
A list of source fields to exclude from the bulk compare.
USING field
A list of source fields to include in the bulk compare. The USING option is a positive version of the EXCEPT option.
TO target
The target database table, buffer, temp-table, or work table.
Directs the AVM to perform a case-sensitive comparison.
Directs the AVM to perform a binary comparison.
SAVE RESULT IN result-field
A variable or field to contain the result of the comparison. The variable or field must be CHARACTER or LOGICAL.
If result-field is CHARACTER, the result is a comma-separated list of fields that failed the comparison, sorted in ascending order.
If result-field is LOGICAL, the result is YES if all fields are equal, or NO if any fields are unequal. In either case, BUFFER-COMPARE stops comparing when it encounters the first inequality.
Opens a block of WHEN options. If you open the block, you must close it with END COMPARES.
WHEN field
Any data field in the source.
BUFFER-COMPARE removes this field from a USING list or adds this field to an EXCEPT list. This removes the field from the bulk compare and from result-field.
Represents one of the following: LT, LE, GT, GE, EQ, NE, MATCHES, BEGINS, or CONTAINS.
Note: For BLOB or CLOB fields, you can only use the EQ (=) or NE (<>) operators.
Any valid ABL expression.
THEN statement-or-block
Any ABL statement or block. The statement or block executes when the WHEN clause evaluates to TRUE.
Closes the block of WHEN phrases.
Directs the AVM to ignore large object data when comparing records that contain BLOB or CLOB fields.
Caution: When using this option, you get no warning if a LOB field has changed. This can lead to inappropriate results. Therefore, before using this option, you must understand the nature of your data and be sure that logic using this option will not result in inconsistent or out-of-date data in the database.
Suppresses ABL errors or error messages that would otherwise occur and diverts them to the ERROR-STATUS system handle. If an error occurs, the action of the statement is not done and execution continues with the next statement. If the statement fails, any persistent side-effects of the statement are backed out. If the statement includes an expression that contains other executable elements, like methods, the work performed by these elements may or may not be done, depending on the order the AVM resolves the expression elements and the occurrence of the error.
To check for errors after a statement that uses the NO-ERROR option:
*Check the ERROR-STATUS:ERROR attribute to see if the AVM raised the ERROR condition.
*Check if the ERROR-STATUS:NUM-MESSAGES attribute is greater than zero to see if the AVM generated error messages. ABL handle methods used in a block without a CATCH end block treat errors as warnings and do not raise ERROR, do not set the ERROR-STATUS:ERROR attribute, but do add messages to the ERROR-STATUS system handle. Therefore, this test is the better test for code using handle methods without CATCH end blocks. ABL handle methods used in a block with a CATCH end block raise ERROR and add messages to the error object generated by the AVM. In this case, the AVM does not update the ERROR-STATUS system handle.
*Use ERROR-STATUS:GET-MESSAGE( message-num ) to retrieve a particular message, where message-num is 1 for the first message.
If the statement does not include the NO-ERROR option, you can use a CATCH end block to handle errors raised by the statement.
Some other important usage notes on the NO-ERROR option:
*NO-ERROR does not suppress errors that raise the STOP or QUIT condition.
*A CATCH statement, which introduces a CATCH end block, is analogous to a NO-ERROR option in that it also suppresses errors, but it does so for an entire block of code. It is different in that the error messages are contained in a class-based error object (generated by the AVM or explicitly thrown), as opposed to the ERROR-STATUS system handle. Also, if errors raised in the block are not handled by a compatible CATCH block, ON ERROR phrase, or UNDO statement, then the error is not suppressed, but handled with the default error processing for that block type.
*When a statement contains the NO-ERROR option and resides in a block with a CATCH end block, the NO-ERROR option takes precedence over the CATCH block. That is, an error raised on the statement with the NO-ERROR option will not be handled by a compatible CATCH end block. The error is redirected to the ERROR-STATUS system handle as normal.
*If an error object is thrown to a statement that includes the NO-ERROR option, then the information and messages in the error object will be used to set the ERROR-STATUS system handle. This interoperability feature is important for those integrating code that uses the traditional NO-ERROR technique with the newer, structured error handling that features error objects and CATCH end blocks.


*At compile time, BUFFER-COMPARE:
*Fails to compile if any source-target field pair is not type compatible. An example of such a pair is a field that is LOGICAL in the source, but DECIMAL in the target.
*Excludes from the bulk comparison all EXCEPT field fields and all WHEN field fields.
*Automatically excludes from the bulk comparison fields that appear in the source but not in the target.
*Tries to bind unqualified field names that appear in the EXCEPT and USING options to the source buffer.
*At run time, BUFFER-COMPARE:
*Compares all fields not in the EXCEPT phrase and all fields not in the WHEN phrase for equality
*Stores the result in the field that the SAVE phrase specifies, if any
*Evaluates each WHEN option, executing it if its condition evaluates to TRUE
Note: This behavior is different from the behavior of the ABL CASE statement, which executes only the first WHEN option whose condition evaluates to TRUE.
*When comparing records that contain BLOB fields, the AVM performs a binary comparison on the BLOB data associated with the source and target records, and reports the results of the comparison.
*You cannot use the BUFFER-COMPARE statement to compare records that contain CLOB fields, unless one or both of the corresponding fields contain the Unknown value (?). However, you can convert CLOB fields to LONGCHAR values and use the EQ, GE, GT, LE, LT, or NE comparison operator to compare the LONGCHAR values.
*The statement supports three types of comparison for CLOB fields, namely, case-sensitive, binary and case-neutral.
*Use the NO-LOBS option with the BUFFER-COMPARE statement to ignore large object data when comparing records that contain BLOB or CLOB fields. You can also use the EXCEPT option to exclude BLOB and CLOB fields from the compare.

See also

BUFFER-COPY statement