Method for remove SQL inquiry statment constant condition

Abstract

The invention is a method for removing the constant condition of the SQL query statement, which includes three steps of creating a linked list, merging the linked list and rewriting the query statement. It converts both CHECK constraints and WHERE conditions into subtrees of the query tree. The leaf nodes are expression nodes, and the other nodes are AND or OR nodes. Postorder traversal is performed on these two subtrees, and an expression node is generated when an expression node is encountered. Column attribute linked list, if an AND or OR node is encountered, the column attribute linked list of the subtree of the node will be merged. In the process of merging linked lists, if a constant true or constant false condition is found, the condition node will be rewritten as a TRUE or FALSE constant node. If the root node of the subtree is finally rewritten as TRUE, the WHERE condition can be removed; if the root node is rewritten as FALSE, the SQL query can be directly rewritten as an empty query. Since the present invention effectively eliminates the constant conditions of SQL query statements at the semantic level, it avoids irrelevant query processing and significantly reduces the processing overhead of the database system executor on the constant true and constant false query conditions.

Description

technical field [0001] The invention relates to a method for rewriting an SQL query statement, in particular to a method for removing constant conditions existing in the SQL query statement by using a linked list. Background technique [0002] In daily applications, databases often need to process large-scale data. Query is an operation frequently used by users. A complex query statement will cause the database system to perform a large amount of tedious data processing. For example, the complexity of the WHERE condition can greatly affect the performance of the database. query speed. [0003] At present, the known database query optimization technologies cannot eliminate complex WHERE constant conditions at the semantic level, which leads to the need for query executors to use WHERE conditions for filtering when scanning each row of the table, thereby greatly increasing data processing overhead. If the query optimizer can eliminate some unnecessary WHERE conditions from th...

AI Technical Summary

Problems solved by technology

[0002] In daily applications, databases often need to process large-scale data. Query is an operation frequently used by users. A complex query statement will cause the database system to perform a large amount of tedious data processing. For example, the complexity of the WHERE condition can greatly affect the performance of the database. query speed

[0003] At present, the known database query optimization technologies cannot eliminate complex WHERE constant conditions at the semantic level, which leads to the query executor needing to use the WHERE condition for filtering when scanning each row of the table, thus greatly increasing the data processing overhead

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