EXPLAIN

In addition to the MySQL standard result format, TiDB also supports DotGraph and you need to specify FORMAT = "dot" as in the following example:

CREATE TABLE t(a bigint, b bigint);
EXPLAIN format = "dot" SELECT A.a, B.b FROM t A JOIN t B ON A.a > B.b WHERE A.a < 10;

+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| dot contents                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|
digraph Projection_8 {
subgraph cluster8{
node [style=filled, color=lightgrey]
color=black
label = "root"
"Projection_8" -> "HashJoin_9"
"HashJoin_9" -> "TableReader_13"
"HashJoin_9" -> "Selection_14"
"Selection_14" -> "TableReader_17"
}
subgraph cluster12{
node [style=filled, color=lightgrey]
color=black
label = "cop"
"Selection_12" -> "TableFullScan_11"
}
subgraph cluster16{
node [style=filled, color=lightgrey]
color=black
label = "cop"
"Selection_16" -> "TableFullScan_15"
}
"TableReader_13" -> "Selection_12"
"TableReader_17" -> "Selection_16"
}
 |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

If your computer has a dot program, you can generate a PNG file using the following method:

dot xx.dot -T png -O

The xx.dot is the result returned by the above statement.

If your computer has no dot program, copy the result to this website to get a tree diagram:

To get the output in JSON, specify FORMAT = "tidb_json" in the EXPLAIN statement. The following is an example:

CREATE TABLE t(id int primary key, a int, b int, key(a));
EXPLAIN FORMAT = "tidb_json" SELECT id FROM t WHERE a = 1;

+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| TiDB_JSON                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| [
    {
        "id": "Projection_4",
        "estRows": "10.00",
        "taskType": "root",
        "operatorInfo": "test.t.id",
        "subOperators": [
            {
                "id": "IndexReader_6",
                "estRows": "10.00",
                "taskType": "root",
                "operatorInfo": "index:IndexRangeScan_5",
                "subOperators": [
                    {
                        "id": "IndexRangeScan_5",
                        "estRows": "10.00",
                        "taskType": "cop[tikv]",
                        "accessObject": "table:t, index:a(a)",
                        "operatorInfo": "range:[1,1], keep order:false, stats:pseudo"
                    }
                ]
            }
        ]
    }
]
 |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

In the output, id, estRows, taskType, accessObject, and operatorInfo have the same meaning as the columns in the default format. subOperators is an array that stores the sub-nodes. The fields and meanings of the sub-nodes are the same as the parent node. If a field is missing, it means that the field is empty.