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EXPLAIN
更新时间：2026-04-07 17:32:32
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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。
EXPLAIN 与 DESCRIBE、DESC 互为同义词。
语法
{EXPLAIN [INTO table_name ] [SET statement_id = string]
| DESCRIBE
| DESC}
[explain_type] [PRETTY | PRETTY_COLOR] dml_statement
explain_type:
BASIC
| OUTLINE
| EXTENDED
| EXTENDED_NOADDR
| PARTITIONS
| FORMAT = {TRADITIONAL| JSON}
dml_statement:
SELECT statement
| DELETE statement
| INSERT statement
| REPLACE statement
| UPDATE statement
参数解释
| 参数 | 描述 |
|---|---|
| INTO table_name | 表示将 EXPLAIN 的计划信息保存到指定表内。如果没有指定 INTO table_name，默认查询到 PLAN_TABLE 表内。 |
| SET statement_id | 表示当前查询使用字符串标记，以方便后续查询该 SQL 的计划信息。如果没有指定 SET statement_id，默认使用空字符串作为信息标记。 |
| PRETTY | PRETTY_COLOR | 将计划树中的父节点和子节点使用树线或彩色树线连接起来，使得执行计划展示更方便阅读。 |
| 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：
|
| dml_statement | DML 语句。 |
示例
解释查询计划，并把计划信息保存在指定表
test内。/* 创建表 test */ obclient> CREATE TABLE test (statement_id VARCHAR(30), plan_id INT, gmt_create TIMESTAMP, remarks VARCHAR(4000), operator VARCHAR(255), options VARCHAR(255), object_node VARCHAR(40), object_owner VARCHAR(128), object_name VARCHAR(128), object_alias VARCHAR(261), object_instance INT, object_type VARCHAR(30),optimizer VARCHAR(4000), search_columns INT, id INT, parent_id INT, depth INT, position INT,is_last_child INT, cost INT, cardinality INT, bytes INT, rowset INT, other_tag VARCHAR(4000), partition_start VARCHAR(4000), partition_stop VARCHAR(4000), partition_id INT, other VARCHAR(4000), distribution VARCHAR(64), cpu_cost INT, io_cost INT, temp_space INT, access_predicates VARCHAR(4000), filter_predicates VARCHAR(4000),startup_predicates VARCHAR(4000), projection VARCHAR(4000), special_predicates VARCHAR(4000), time INT, qblock_name VARCHAR(128), other_xml VARCHAR(4000)); obclient> CREATE TABLE t1(c1 INT); /* 解释查询计划，并把计划信息保存在指定表 test 内 */ obclient> EXPLAIN INTO test SELECT COUNT(*) FROM t1; +--------------------------------------------------------------------------+ | Query Plan | +--------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |SCALAR GROUP BY | |1 |2 | | | |1 |└─TABLE FULL SCAN|t1 |1 |2 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]), filter(nil), rowset=256 | | group(nil), agg_func([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]) | | 1 - output([T_FUN_COUNT(*)]), filter(nil), rowset=256 | | access(nil), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([t1.__pk_increment]), range(MIN ; MAX)always true | +--------------------------------------------------------------------------+ 14 rows in set obclient> SELECT DBMS_XPLAN.DISPLAY('TYPICAL',null,'test')\G *************************** 1. row *************************** DBMS_XPLAN.DISPLAY('TYPICAL',null,'test'): ================================================= |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| ------------------------------------------------- |0 |SCALAR GROUP BY | |1 |2 | |1 |└─TABLE FULL SCAN|t1 |1 |2 | ================================================= Outputs & filters: ------------------------------------- 0 - output([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]), filter(nil), rowset=256 group(nil), agg_func([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]) 1 - output([T_FUN_COUNT(*)]), filter(nil), rowset=256 access(nil), partitions(p0) is_index_back=false, is_global_index=false, range_key([t1.__pk_increment]), range(MIN ; MAX)always true 1 row in set解释查询计划，并为查询设置标识信息。
obclient> EXPLAIN INTO test SET statement_id='test2' SELECT COUNT(*) FROM t1; +--------------------------------------------------------------------------+ | Query Plan | +--------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |SCALAR GROUP BY | |1 |2 | | | |1 |└─TABLE FULL SCAN|t1 |1 |2 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]), filter(nil), rowset=256 | | group(nil), agg_func([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]) | | 1 - output([T_FUN_COUNT(*)]), filter(nil), rowset=256 | | access(nil), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([t1.__pk_increment]), range(MIN ; MAX)always true | +--------------------------------------------------------------------------+ 14 rows in set obclient> SELECT DBMS_XPLAN.DISPLAY('TYPICAL','test2','test')\G *************************** 1. row *************************** DBMS_XPLAN.DISPLAY('TYPICAL','test2','test'): ================================================= |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| ------------------------------------------------- |0 |SCALAR GROUP BY | |1 |2 | |1 |└─TABLE FULL SCAN|t1 |1 |2 | ================================================= Outputs & filters: ------------------------------------- 0 - output([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]), filter(nil), rowset=256 group(nil), agg_func([T_FUN_COUNT_SUM(T_FUN_COUNT(*))]) 1 - output([T_FUN_COUNT(*)]), filter(nil), rowset=256 access(nil), partitions(p0) is_index_back=false, is_global_index=false, range_key([t1.__pk_increment]), range(MIN ; MAX)always true 1 row in set省略
explain_type，返回语句的执行计划。obclient> EXPLAIN SELECT * FROM t1,t2 WHERE t1.c2=t2.c2 AND t2.c1 > 4; +------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |HASH JOIN | |1 |9 | | | |1 |├─TABLE FULL SCAN|t2 |1 |4 | | | |2 |└─TABLE FULL SCAN|t1 |2 |4 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), rowset=16 | | equal_conds([t1.c2 = t2.c2]), other_conds(nil) | | 1 - output([t2.c2], [t2.c1]), filter([t2.c1 > 4]), rowset=16 | | access([t2.c2], [t2.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, filter_before_indexback[false], | | range_key([t2.__pk_increment]), range(MIN ; MAX)always true | | 2 - output([t1.c2], [t1.c1]), filter(nil), rowset=16 | | access([t1.c2], [t1.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([t1.__pk_increment]), range(MIN ; MAX)always true | +------------------------------------------------------------------------------------+通过
EXTENDED_NOADDR关键字输出附加信息。obclient> EXPLAIN EXTENDED_NOADDR SELECT * FROM t1,t2 WHERE t1.c2=t2.c2 AND t2.c1 > 4; +------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |HASH JOIN | |1 |9 | | | |1 |├─TABLE FULL SCAN|t2 |1 |4 | | | |2 |└─TABLE FULL SCAN|t1 |2 |4 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), rowset=16 | | equal_conds([t1.c2 = t2.c2]), other_conds(nil) | | 1 - output([t2.c2], [t2.c1]), filter([t2.c1 > 4]), rowset=16 | | access([t2.c2], [t2.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, filter_before_indexback[false], | | range_key([t2.__pk_increment]), range(MIN ; MAX)always true | | 2 - output([t1.c2], [t1.c1]), filter(nil), rowset=16 | | access([t1.c2], [t1.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([t1.__pk_increment]), range(MIN ; MAX)always true | | Used Hint: | | ------------------------------------- | | /*+ | | | | */ | | Qb name trace: | | ------------------------------------- | | stmt_id:0, stmt_type:T_EXPLAIN | | stmt_id:1, SEL$1 | | Outline Data: | | ------------------------------------- | | /*+ | | BEGIN_OUTLINE_DATA | | LEADING(@"SEL$1" ("mysql"."t2"@"SEL$1" "mysql"."t1"@"SEL$1")) | | USE_HASH(@"SEL$1" "mysql"."t1"@"SEL$1") | | FULL(@"SEL$1" "mysql"."t2"@"SEL$1") | | FULL(@"SEL$1" "mysql"."t1"@"SEL$1") | | OPTIMIZER_FEATURES_ENABLE('4.0.0.0') | | END_OUTLINE_DATA | | */ | | Optimization Info: | | ------------------------------------- | | t2: | | table_rows:3 | | physical_range_rows:3 | | logical_range_rows:3 | | index_back_rows:0 | | output_rows:0 | | table_dop:1 | | dop_method:Table DOP | | avaiable_index_name:[t2] | | stats version:0 | | dynamic sampling level:1 | | t1: | | table_rows:2 | | physical_range_rows:2 | | logical_range_rows:2 | | index_back_rows:0 | | output_rows:2 | | table_dop:1 | | dop_method:Table DOP | | avaiable_index_name:[t1] | | stats version:0 | | dynamic sampling level:1 | | Plan Type: | | LOCAL | | Note: | | Degree of Parallelisim is 1 because of table property | +------------------------------------------------------------------------------------+展示
TRADITIONAL格式的执行计划。obclient> EXPLAIN FORMAT=TRADITIONAL SELECT * FROM t1,t2 WHERE t1.c2=t2.c2 AND t2.c1 > 4; +------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |HASH JOIN | |1 |9 | | | |1 |├─TABLE FULL SCAN|t2 |1 |4 | | | |2 |└─TABLE FULL SCAN|t1 |2 |4 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([t1.c1], [t1.c2], [t2.c1], [t2.c2]), filter(nil), rowset=16 | | equal_conds([t1.c2 = t2.c2]), other_conds(nil) | | 1 - output([t2.c2], [t2.c1]), filter([t2.c1 > 4]), rowset=16 | | access([t2.c2], [t2.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, filter_before_indexback[false], | | range_key([t2.__pk_increment]), range(MIN ; MAX)always true | | 2 - output([t1.c2], [t1.c1]), filter(nil), rowset=16 | | access([t1.c2], [t1.c1]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([t1.__pk_increment]), range(MIN ; MAX)always true | +------------------------------------------------------------------------------------+展示
JSON格式的执行计划。obclient> EXPLAIN FORMAT=JSON SELECT * FROM t1,t2 WHERE t1.c2=t2.c2 AND t2.c1 > 4; +----------------------------------------------------------+ | Query Plan | +----------------------------------------------------------+ | { | | "ID":0, | | "OPERATOR":"HASH JOIN ", | | "NAME":"", | | "EST.ROWS":1, | | "EST.TIME(us)":9, | | "output":"output([t1.c1], [t1.c2], [t2.c1], [t2.c2])", | | "CHILD_1": { | | "ID":1, | | "OPERATOR":"TABLE FULL SCAN", | | "NAME":"t2", | | "EST.ROWS":1, | | "EST.TIME(us)":4, | | "output":"output([t2.c2], [t2.c1])" | | }, | | "CHILD_2": { | | "ID":2, | | "OPERATOR":"TABLE FULL SCAN", | | "NAME":"t1", | | "EST.ROWS":2, | | "EST.TIME(us)":4, | | "output":"output([t1.c2], [t1.c1])" | | } | | } | +----------------------------------------------------------+解释
UPDATE语句的执行计划。obclient> CREATE TABLE employees (emp_id INT PRIMARY KEY, emp_name VARCHAR(50), salary INT); obclient> INSERT INTO employees VALUES (1, 'Alice', 5000), (2, 'Bob', 6000); obclient> EXPLAIN UPDATE employees SET salary = salary * 1.1 WHERE emp_id > 1;执行结果如下：
+--------------------------------------------------------------------------------------------------------------+ | Query Plan | +--------------------------------------------------------------------------------------------------------------+ | ======================================================= | | |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| | | ------------------------------------------------------- | | |0 |UPDATE | |1 |34 | | | |1 |└─TABLE RANGE SCAN|employees|1 |3 | | | ======================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output(nil), filter(nil) | | table_columns([{employees: ({employees: (employees.emp_id, employees.emp_name, employees.salary)})}]), | | update([employees.salary=column_conv(INT,PS:(11,0),NULL,cast(employees.salary * 1.1, INT(-1, 0)))]) | | 1 - output([employees.emp_id], [employees.salary], [employees.emp_name]), filter(nil), rowset=16 | | access([employees.emp_id], [employees.salary], [employees.emp_name]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([employees.emp_id]), range(1 ; MAX), | | range_cond([employees.emp_id > 1]) | +--------------------------------------------------------------------------------------------------------------+解释
INSERT语句的执行计划。obclient> EXPLAIN INSERT INTO employees VALUES (3, 'Charlie', 7000);执行结果如下：
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Query Plan | +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | ================================================== | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | -------------------------------------------------- | | |0 |DISTRIBUTED INSERT| |1 |13 | | | |1 |└─EXPRESSION | |1 |1 | | | ================================================== | | Outputs & filters: | | ------------------------------------- | | 0 - output(nil), filter(nil) | | columns([{employees: ({employees: (employees.emp_id, employees.emp_name, employees.salary)})}]), | | column_values([column_conv(INT,PS:(11,0),NOT NULL,__values.emp_id)], [column_conv(VARCHAR,utf8mb4_general_ci,length:50,NULL,__values.emp_name)], [column_conv(INT, | | PS:(11,0),NULL,__values.salary)]) | | 1 - output([__values.emp_id], [__values.emp_name], [__values.salary]), filter(nil) | | values({3, 'Charlie', 7000}) | +--------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
