Which best Mysql index

Question

Hello I have a question about explain, index in mysql

Real Estate Table 47.240 Table of Order of Attendance 1,887,421

SELECT
    SQL_NO_CACHE
    COUNT(*)
FROM
    imoveis I
    INNER JOIN situacao_cod_venda SCV   ON SCV.flag_mostra_site     = 1 AND SCV.id  = I.situacao_codigo_venda
WHERE 
    NOT EXISTS 
    (
        SELECT 
            id 
        FROM 
            ordem_atendimento_envio OAE 
        WHERE 
            I.data_alt_sit_ven = OAE.data_ultima_alteracao_situacao AND 
            OAE.id_imovel = I.id AND 
            OAE.id_ordem_atendimento = '69451' 
    )

when I create the index for id_imovel of the table order of service explain shows me 9438 and the query takes 5 seconds

when I create the index for id_ordem_attendance table order the explain shows me 478 and the query takes 15 seconds

in the immovable table in explain both returns 48253

when I create a compound index id_imovel, id_ordem_response is instantaneous, no second 0.412 milestones of seconds, but explain shows 9438.

Would you like to know why the index that got smaller got slower? What is the rule for checking checked lines ex: explain table immovable Rows 48253 table order Contact Rows 478

then checked Rows is 48253*478 = 23.064.934 (would that be?)

What sifinifies when ref leaves null, or const

see the video below that I exemplified in detail.

Mysql behavior makes no sense (VIDEO ON VIMEO)

Indice with less registration, slower.

Hugs