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EXPLAIN
更新时间：2024-08-01 16:31:34
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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
/*获取表或列的信息*/
{EXPLAIN | DESCRIBE | DESC} table_name [column_name];
/*获取 SQL 计划信息*/
{EXPLAIN | DESCRIBE | DESC} [explain_type] dml_statement;
explain_type：
BASIC
| OUTLINE
| EXTENDED
| EXTENDED_NOADDR
| PARTITIONS
| FORMAT = {TRADITIONAL| JSON}
dml_statement:
SELECT statement
| DELETE statement
| INSERT statement
| UPDATE statement
| MERGE statement
参数解释
| 参数 | 描述 |
|---|---|
| table_name | 指定表名。 |
| column_name | 指定表的列名。 |
| explain_type | 指定解释类型。 |
| BASIC | 指定输出计划的基础信息，例如算子 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。 |
| TRADITIONAL | JSON | 指定 EXPALIN 的输出格式。
|
| dml_statement | DML 声明。 |
示例
创建示例表 t101 和 t102。
obclient> CREATE TABLE t101(c1 INT,c2 INT);
Query OK, 0 rows affected
obclient> CREATE TABLE t102(c1 INT,c2 INT);
Query OK, 0 rows affected
获取表
t101的信息。obclient> EXPLAIN t101; +-------+------------+------+-----+---------+-------+ | FIELD | TYPE | NULL | KEY | DEFAULT | EXTRA | +-------+------------+------+-----+---------+-------+ | C1 | NUMBER(38) | YES | NULL | NULL | NULL | | C2 | NUMBER(38) | YES | NULL | NULL | NULL | +-------+------------+------+-----+---------+-------+ 2 rows in set获取表
t102的列c2的信息。obclient> EXPLAIN t102 c2; +-------+------------+------+-----+---------+-------+ | FIELD | TYPE | NULL | KEY | DEFAULT | EXTRA | +-------+------------+------+-----+---------+-------+ | C2 | NUMBER(38) | YES | NULL | NULL | NULL | +-------+------------+------+-----+---------+-------+ 1 row in set省略
explain_type，返回SELECT语句的执行计划信息。obclient> EXPLAIN SELECT * FROM t101,t102 WHERE t101.c2=t102.c2 AND t102.c1 > 4; +------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |HASH JOIN | |1 |8 | | | |1 |├─TABLE FULL SCAN|T102|1 |4 | | | |2 |└─TABLE FULL SCAN|T101|1 |4 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([T101.C1], [T101.C2], [T102.C1], [T102.C2]), filter(nil), rowset=16 | | equal_conds([T101.C2 = T102.C2]), other_conds(nil) | | 1 - output([T102.C2], [T102.C1]), filter([T102.C1 > 4]), rowset=16 | | access([T102.C2], [T102.C1]), partitions(p0) | | is_index_back=false, is_global_index=false, filter_before_indexback[false], | | range_key([T102.__pk_increment]), range(MIN ; MAX)always true | | 2 - output([T101.C2], [T101.C1]), filter(nil), rowset=16 | | access([T101.C2], [T101.C1]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([T101.__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 t101,t102 WHERE t101.c2=t102.c2 AND t102.c1 > 4; +------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------+ | ================================================= | | |ID|OPERATOR |NAME|EST.ROWS|EST.TIME(us)| | | ------------------------------------------------- | | |0 |HASH JOIN | |1 |8 | | | |1 |├─TABLE FULL SCAN|T102|1 |4 | | | |2 |└─TABLE FULL SCAN|T101|1 |4 | | | ================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output([T101.C1], [T101.C2], [T102.C1], [T102.C2]), filter(nil), rowset=16 | | equal_conds([T101.C2 = T102.C2]), other_conds(nil) | | 1 - output([T102.C2], [T102.C1]), filter([T102.C1 > 4]), rowset=16 | | access([T102.C2], [T102.C1]), partitions(p0) | | is_index_back=false, is_global_index=false, filter_before_indexback[false], | | range_key([T102.__pk_increment]), range(MIN ; MAX)always true | | 2 - output([T101.C2], [T101.C1]), filter(nil), rowset=16 | | access([T101.C2], [T101.C1]), partitions(p0) | | is_index_back=false, is_global_index=false, | | range_key([T101.__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" ("SYS"."T102"@"SEL$1" "SYS"."T101"@"SEL$1")) | | USE_HASH(@"SEL$1" "SYS"."T101"@"SEL$1") | | FULL(@"SEL$1" "SYS"."T102"@"SEL$1") | | FULL(@"SEL$1" "SYS"."T101"@"SEL$1") | | OPTIMIZER_FEATURES_ENABLE('4.0.0.0') | | END_OUTLINE_DATA | | */ | | Optimization Info: | | ------------------------------------- | | T102: | | table_rows:1 | | physical_range_rows:1 | | logical_range_rows:1 | | index_back_rows:0 | | output_rows:0 | | table_dop:1 | | dop_method:Table DOP | | avaiable_index_name:[T102] | | stats version:0 | | dynamic sampling level:1 | | T101: | | table_rows:1 | | physical_range_rows:1 | | logical_range_rows:1 | | index_back_rows:0 | | output_rows:1 | | table_dop:1 | | dop_method:Table DOP | | avaiable_index_name:[T101] | | 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INSERT语句执行计划。obclient> EXPLAIN FORMAT=TRADITIONAL INSERT INTO T101 VALUES(1,1); +----------------------------------------------------------------------------------------------------------------------------------------+ | 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([{T101: ({T101: (T101.__pk_increment, T101.C1, T101.C2)})}]), | | column_values([T_HIDDEN_PK], [column_conv(NUMBER,PS:(-1,0),NULL,__values.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,__values.C2)]) | | 1 - output([__values.C1], [__values.C2]), filter(nil) | | values({1, 1}) | +----------------------------------------------------------------------------------------------------------------------------------------+展示
JSON格式的SELECT语句执行计划。obclient> EXPLAIN FORMAT=JSON SELECT * FROM t101,t102 WHERE t101.c2=t102.c2 AND t102.c1 > 4; +------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------+ | { | | "ID":0, | | "OPERATOR":"HASH JOIN ", | | "NAME":"", | | "EST.ROWS":1, | | "EST.TIME(us)":8, | | "output":"output([T101.C1], [T101.C2], [T102.C1], [T102.C2])", | | "CHILD_1": { | | "ID":1, | | "OPERATOR":"TABLE FULL SCAN", | | "NAME":"T102", | | "EST.ROWS":1, | | "EST.TIME(us)":4, | | "output":"output([T102.C2], [T102.C1])" | | }, | | "CHILD_2": { | | "ID":2, | | "OPERATOR":"TABLE FULL SCAN", | | "NAME":"T101", | | "EST.ROWS":1, | | "EST.TIME(us)":4, | | "output":"output([T101.C2], [T101.C1])" | | } | | } | +------------------------------------------------------------------+
