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。
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 | 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：
|
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)
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
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)
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。 |
备案信息： 粤ICP备15087711号-2
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