create or replace table t1 (a int, b int, c int, key(a,c), key(b,c), key (c,b)) engine=aria;
insert into t1 select seq/100+1, mod(seq,10), mod(seq,15) from seq_1_to_10000;
insert into t1 select seq/100+1, mod(seq,10), 10 from seq_1_to_1000;
optimize table t1;
Table	Op	Msg_type	Msg_text
test.t1	optimize	status	OK
select count(*) from t1 where a=2;
count(*)
200
select count(*) from t1 where b=5;
count(*)
1100
select count(*) from t1 where c=5;
count(*)
667
select count(*) from t1 where c=10;
count(*)
1667
select count(*) from t1 where a=2 and b=5;
count(*)
20
select count(*) from t1 where c=10 and b=5;
count(*)
433
select count(*) from t1 where c=5 and b=5;
count(*)
334
set optimizer_trace="enabled=on";
select count(*) from t1 where a=2 and b=5 and c=10;
count(*)
14
set @trace=(select trace from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
select 
JSON_DETAILED(
JSON_EXTRACT(
JSON_EXTRACT(@trace, '$**.considered_execution_plans'),
'$[0]'
    )
) as JS;
JS
[
    {
        "plan_prefix": "",
        "get_costs_for_tables": 
        [
            {
                "best_access_path": 
                {
                    "table": "t1",
                    "plan_details": 
                    {
                        "record_count": 1
                    },
                    "considered_access_paths": 
                    [
                        {
                            "access_type": "ref",
                            "index": "a",
                            "used_range_estimates": true,
                            "rows": 104,
                            "cost": 0.060988785,
                            "chosen": true
                        },
                        {
                            "access_type": "ref",
                            "index": "b",
                            "used_range_estimates": true,
                            "rows": 340,
                            "cost": 0.141618657,
                            "chosen": false,
                            "cause": "cost"
                        },
                        {
                            "access_type": "ref",
                            "index": "c",
                            "used_range_estimates": true,
                            "rows": 632,
                            "cost": 0.241826241,
                            "chosen": false,
                            "cause": "cost"
                        },
                        {
                            "access_type": "index_merge",
                            "rows": 7,
                            "rows_after_filter": 7,
                            "rows_out": 7,
                            "cost": 0.045367017,
                            "chosen": true
                        }
                    ],
                    "chosen_access_method": 
                    {
                        "type": "index_merge",
                        "rows_read": 7,
                        "rows_out": 7,
                        "cost": 0.045367017,
                        "uses_join_buffering": false
                    }
                }
            }
        ]
    },
    {
        "plan_prefix": "",
        "table": "t1",
        "rows_for_plan": 7,
        "cost_for_plan": 0.045367017
    }
]
select JSON_DETAILED(JSON_EXTRACT(@trace, '$**.selectivity_for_indexes')) as JS;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.009454545
        },
        {
            "index_name": "b",
            "selectivity_from_index": 0.1
        },
        {
            "use_opt_range_condition_rows_selectivity": 6.363636e-4
        }
    ]
]
select count(*) from t1 where a=2 and b=5 and c=5;
count(*)
3
set @trace=(select trace from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
select 
JSON_DETAILED(
JSON_EXTRACT(
JSON_EXTRACT(@trace, '$**.considered_execution_plans'),
'$[0]'
    )
) as JS;
JS
[
    {
        "plan_prefix": "",
        "get_costs_for_tables": 
        [
            {
                "best_access_path": 
                {
                    "table": "t1",
                    "plan_details": 
                    {
                        "record_count": 1
                    },
                    "considered_access_paths": 
                    [
                        {
                            "access_type": "ref",
                            "index": "a",
                            "used_range_estimates": true,
                            "rows": 6,
                            "cost": 0.005388489,
                            "chosen": true
                        },
                        {
                            "access_type": "ref",
                            "index": "b",
                            "used_range_estimates": true,
                            "rows": 232,
                            "cost": 0.104720241,
                            "chosen": false,
                            "cause": "cost"
                        },
                        {
                            "access_type": "ref",
                            "index": "c",
                            "used_range_estimates": true,
                            "rows": 293,
                            "cost": 0.125561013,
                            "chosen": false,
                            "cause": "cost"
                        },
                        {
                            "type": "scan",
                            "chosen": false,
                            "cause": "cost"
                        }
                    ],
                    "chosen_access_method": 
                    {
                        "type": "ref",
                        "rows_read": 6,
                        "rows_out": 0.6,
                        "cost": 0.005388489,
                        "uses_join_buffering": false
                    }
                }
            }
        ]
    },
    {
        "plan_prefix": "",
        "table": "t1",
        "rows_for_plan": 0.6,
        "cost_for_plan": 0.005388489,
        "pushdown_cond_selectivity": 0.1,
        "filtered": 10,
        "rows_out": 0.6
    }
]
select JSON_DETAILED(JSON_EXTRACT(@trace, '$**.selectivity_for_indexes')) as JS;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 5.454545e-4
        },
        {
            "index_name": "b",
            "selectivity_from_index": 0.1
        }
    ]
]
# Ensure that we only use selectivity from non used index for simple cases
select count(*) from t1 where (a=2 and b= 5);
count(*)
20
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.017545455
        },
        {
            "index_name": "b",
            "selectivity_from_index": 0.073181818
        }
    ]
]
# All of the following should have selectivity=1 for index 'b'
select count(*) from t1 where (a=2 and b between 0 and 100);
count(*)
200
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.017545455
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a in (2,3) and b between 0 and 100);
count(*)
400
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.035090909
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a>2 and b between 0 and 100);
count(*)
10702
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.973909091
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a>=2 and b between 0 and 100);
count(*)
10902
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.991454545
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a<=2 and b between 0 and 100);
count(*)
298
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.026181818
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a<2 and b between 0 and 100);
count(*)
98
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.008636364
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
select count(*) from t1 where (a between 2 and 3 and b between 0 and 100);
count(*)
400
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_indexes')) as JS
from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
    [
        {
            "index_name": "a",
            "selectivity_from_index": 0.035090909
        },
        {
            "index_name": "b",
            "selectivity_from_index": 1
        }
    ]
]
drop table t1;
set optimizer_trace='enabled=off';