explain的作用: 判断mysql语句执行的时间效率分析;1、在navicate客户端使用sql语句的时候,整体图形如下2、名词解释 一、select_type数据列指明各“单位...在一起。MariaDB中,不会在默认优化器模式下先处理IN(subquery)查询内部的子查询,而是读取外部的employees数据表,再执行子查询时,dependent关键字就会出现在select_...
Oracle 数据库中优化器(Optimizer)是SQL分析和执行的优化工具,它负责指定SQL的执行计划,也就是它负责保证SQL执行的效率最高,比如优化器决定Oracle 以什么样的方式来访问数据,是全表扫描(Full Table Scan),索引范围扫描(Index Range Scan)还是全索引快速扫描(INDEX Fast Full Scan:INDEX_FFS);对于表关联查询,它负责...
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
Reimplemented inExplain_format_JSON, andExplain_format_tree. virtual bool Explain_format::flush_entry() pure virtual Flush TABLE/JOIN_TAB property set. For traditional EXPLAIN: output a single EXPLAIN row. Implemented inExplain_format_JSON,Explain_format_traditional, andExplain_format_tree. ...
ExplainPropertyBool("Single Copy", gather->single_copy, es); } break; case T_GatherMerge: { GatherMerge *gm = (GatherMerge *) plan; show_scan_qual(plan->qual, "Filter", planstate, ancestors, es); if (plan->qual) show_instrumentation_count("Rows Removed by Filter", 1, planstate,...
3、flink sql cli 示例 二、EXPLAIN 语句 1、语法 2、java 示例 1、maven依赖 2)、java 代码 3)、运行结果 3、flink sql cli示例 1)、建表 2)、EXPLAIN PLAN FOR执行计划查询及结果 2)、EXPLAIN ESTIMATED_COST, CHANGELOG_MODE, PLAN_ADVICE, JSON_EXECUTION_PLAN执行计划查询及结果 4、ExplainDetails 1)...
LAG(column)returns the value ofcolumnfrom the previous row in the grouping set, orNULLif there is no previous row. LEAD(column)returns the value ofcolumnfrom the next row in the grouping set, orNULLif there is no next row. ? 1
REPLICATE –Copies the row data to all workers. Distributed Exchange types The following exchange types indicate the layout of the data when they are exchanged between nodes in a distributed plan. HASH –The exchange distributes data to multiple destinations using a hash function. SINGLE –The exc...
1 row in set (0.00 sec) mysql>explain select * from user whereUser='root' \G *** 1. row*** id: 1 select_type: SIMPLE table: user type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 7 Extra: Using where 1 row...
If SQL query performance is poor or query results do not meet expectations, you can execute the EXPLAIN and EXPLAIN ANALYZE statements in Hologres to obtain execution plans of query statements. This way, you can optimize query statements or database structures. This topic describes how to execute...