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This patch introduces a new way of handling UPDATE and DELETE commands at the top level after the parsing phase. This new way of processing update and delete statements can be seen in the implementation of the prepare() and execute() methods from the new Sql_cmd_dml class. This class derived from the Sql_cmd class can be considered as an interface class for processing such commands as SELECT, INSERT, UPDATE, DELETE and other comands manipulating data in tables. With this patch processing of update and delete statements after parsing proceeds by the following schema: - precheck of the access rights is performed for the used tables - the used tables are opened - context analysis phase is performed for the statement - the used tables are locked - the statement is optimized and executed - clean-up is performed for the statement The implementation of the method Sql_cmd_dml::execute() adheres this schema. The virtual functions of the class Sql_cmd_dml used for precheck of the access rights, context analysis, optimization and execution allow to adjust this schema for processing data manipulation statements of any types. This schema of processing data manipulation statements is taken from the current MySQL code. Moreover the definition the class Sql_cmd_dml introduced in this patch is almost a full replica of such class in the existing MySQL. However the implementation of the derived classes for update and delete statements is quite different. This implementation employs the JOIN class for all kinds of update and delete statements. It allows to perform main bulk of context analysis actions by the function JOIN::prepare(). This guarantees that characteristics and properties of the statement tree discovered for optimization phase when doing context analysis are the same for single-table and multi-table updates and deletes. With this patch the following functions are gone: mysql_prepare_update(), mysql_multi_update_prepare(), mysql_update(), mysql_multi_update(), mysql_prepare_delete(), mysql_multi_delete_prepare(), mysql_delete(). The code within these functions have been used as much as possible though. The functions mysql_test_update() and mysql_test_delete() are also not needed anymore. The method Sql_cmd_dml::prepare() serves processing - update/delete statement - PREPARE stmt FROM "<update/delete statement>" - EXECUTE stmt when stmt is prepared from update/delete statement. Approved by Oleksandr Byelkin <sanja@mariadb.com> |
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