H2 Database 简明教程

H2 Database - Explain

EXPLAIN 命令显示语句的执行计划。当我们使用 EXPLAIN ANALYZE 命令执行语句时，查询计划将包括每个表的实际行扫描计数。

EXPLAIN command displays the execution plan for a statement. When we execute a statement using EXPLAIN ANALYZE command, the query plan will include the actual row scan count for each table.

Syntax

以下是 EXPLAIN 命令的通用语法。

Following is the generic syntax of the EXPLAIN command.

EXPLAIN { [ PLAN FOR ] | ANALYZE } { select | insert | update | delete | merge}

除了此语法，我们还可以使用 select，insert，delete 和 merge。

Along with this syntax we can use select, insert, delete, and merge.

Example

此示例说明了具有 ID 1 的客户的查询计划详细信息。

This example explains the query plan details of the customer with ID 1.

EXPLAIN SELECT * FROM CUSTOMER WHERE ID = 1;

以上命令生成以下输出 −

The above command produces the following output −

explain output