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create or replace table t1 (col1 char(10) character set ucs2, filler char(100), key(col1)) ;
insert into t1 values ('a', 'a');
insert into t1 values ('a', 'a');
set optimizer_trace=1;
explain format=json select * from t1 force index(col1) where col1 >='a';
EXPLAIN
{
"query_block": {
"select_id": 1,
"cost": "COST_REPLACED",
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["col1"],
"key": "col1",
"key_length": "21",
"used_key_parts": ["col1"],
"loops": 1,
"rows": 2,
"cost": "COST_REPLACED",
"filtered": 100,
"index_condition": "t1.col1 >= 'a'"
}
}
]
}
}
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
{
"range_scan_alternatives":
[
{
"index": "col1",
"ranges":
["(a) <= (col1)"],
"rowid_ordered": false,
"using_mrr": false,
"index_only": false,
"rows": 2,
"cost": 0.003808422,
"chosen": true
}
],
"analyzing_roworder_intersect":
{
"cause": "too few roworder scans"
},
"analyzing_index_merge_union":
[]
}
]
drop table t1;
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