EXPLAIN ============================ 描述 ----------- 该语句用于解释 SQL 语句的执行计划，可以是SELECT、DELETE、INSERT、REPLACE或UPDATE语句。提供正则过滤功能，通过session变量explain_regex对输出行/JSON进行过滤。 格式 ----------- ```javascript 获取表或列的信息： {EXPLAIN | DESCRIBE | DESC} tbl_name [col_name | wild] 获取SQL计划信息： {EXPLAIN | DESCRIBE | DESC} [BASIC | OUTLINE | EXTENDED | EXTENDED_NOADDR | PARTITIONS | FORMAT = {TRADITIONAL| JSON}] {SELECT statement | DELETE statement | INSERT statement | REPLACE statement| UPDATE statement} ``` 参数解释 ------------- | **参数** | **描述** | |-------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | tbl_name | 指定表名。 | | col_name | 指定表的列名。 | | BASIC | 指定输出计划的基础信息，如算子ID、算子名称、所引用的表名。 | | OUTLINE | 指定输出的计划信息包含outline信息。 | | EXTENDED | EXPLAIN产生附加信息，包括：每个算子的输入列和输出列，访问表的分区信息，当前使用的filter信息，如果当前算子使用了索引，显示所使用的索引列及抽取的query range。 | | EXTENDED_NOADDR | 以简约的方式展示附加信息。 | | PARTITIONS | 显示分区相关信息。 | | FORMAT = {TRADITIONAL\| JSON} | 指定EXPALIN的输出格式： * TRADITIONAL：表格输出格式 * JSON：KEY:VALUE输出格式, JSON显示为JSON字符串，包括EXTENDED和PARTITIONS信息。 | 示例 ----------- * **省略explain_type** ```javascript OceanBase(admin@test)>explain select * from t1,t2 where t1.c2=t2.c2 and t2.c1 > 4\G *************************** 1. row *************************** Query Plan: ======================================= |ID|OPERATOR |NAME|EST. ROWS|COST | --------------------------------------- |0 |HASH JOIN | |9801000 |5933109| |1 | TABLE SCAN|t2 |10000 |6219 | |2 | TABLE SCAN|t1 |100000 |68478 | ======================================= Outputs & filters: ------------------------------------- 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), equal_conds([t1.c2 = t2.c2]), other_conds(nil) 1 - output([t2.c2], [t2.c1]), filter(nil), access([t2.c2], [t2.c1]), partitions(p0) 2 - output([t1.c2], [t1.c1]), filter(nil), access([t1.c2], [t1.c1]), partitions(p0) ``` * **EXTENDED** ```javascript OceanBase(admin@test)>explain extended_noaddr select * from t1,t2 where t1.c2=t2.c2 and t2.c1 > 4\G *************************** 1. row *************************** Query Plan: ======================================= |ID|OPERATOR |NAME|EST. ROWS|COST | --------------------------------------- |0 |HASH JOIN | |9801000 |5933109| |1 | TABLE SCAN|t2 |10000 |6219 | |2 | TABLE SCAN|t1 |100000 |68478 | ======================================= Outputs & filters: ------------------------------------- 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), equal_conds([t1.c2 = t2.c2]), other_conds(nil) 1 - output([t2.c2], [t2.c1]), filter(nil), access([t2.c2], [t2.c1]), partitions(p0), is_index_back=false, range_key([t2.c1]), range(4 ; MAX), range_cond([t2.c1 > 4]) 2 - output([t1.c2], [t1.c1]), filter(nil), access([t1.c2], [t1.c1]), partitions(p0), is_index_back=false, range_key([t1.__pk_increment], [t1.__pk_cluster_id], [t1.__pk_partition_id]), range(MIN,MIN,MIN ; MAX,MAX,MAX)always true ``` * **TRADITIONAL** **格式** ```javascript OceanBase(admin@test)>explain format=TRADITIONAL select * from t1,t2 where t1.c2=t2.c2 and t2.c1 > 4\G *************************** 1. row *************************** Query Plan: ======================================= |ID|OPERATOR |NAME|EST. ROWS|COST | --------------------------------------- |0 |HASH JOIN | |9801000 |5933109| |1 | TABLE SCAN|t2 |10000 |6219 | |2 | TABLE SCAN|t1 |100000 |68478 | ======================================= Outputs & filters: ------------------------------------- 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), equal_conds([t1.c2 = t2.c2]), other_conds(nil) 1 - output([t2.c2], [t2.c1]), filter(nil), access([t2.c2], [t2.c1]), partitions(p0) 2 - output([t1.c2], [t1.c1]), filter(nil), access([t1.c2], [t1.c1]), partitions(p0) ``` * **JSON格式** ```javascript OceanBase(admin@test)>explain format=JSON select * from t1,t2 where t1.c2=t2.c2 and t2.c1 > 4\G *************************** 1. row *************************** Query Plan: { "ID":2, "OPERATOR":"JOIN", "NAME":"JOIN", "EST.ROWS":9800999, "COST":5933108, "output": [ "t1.c1", "t1.c2", "t2.c1", "t2.c2" ], "TABLE SCAN": { "ID":0, "OPERATOR":"TABLE SCAN", "NAME":"TABLE SCAN", "EST.ROWS":10000, "COST":6218, "output": [ "t2.c2", "t2.c1" ] }, "TABLE SCAN": { "ID":1, "OPERATOR":"TABLE SCAN", "NAME":"TABLE SCAN", "EST.ROWS":100000, "COST":68477, "output": [ "t1.c2", "t1.c1" ] } } ``` EXPLAIN 的每个输出行提供一个表的相关信息，并且每个行包括下面的列： | **列名** | **说明** | |----------|-----------------| | ID | 计划执行序列号。 | | OPERATOR | 执行算子。 | | NAME | 算子所引用的表。 | | EST.ROWS | 估计执行到当前算子输出的行数。 | | COST | 执行到当前算子的CPU时间。 |