我执行以下查询
EXPLAIN
SELECT *
FROM firmware_versions
WHERE serial_number = '123'
AND hardware_version = 'version-1'
AND firmware_type = 'avr'
ORDER BY creation_time DESC
LIMIT 1
唯一索引超过(serial_number, hardware_version, firmware_type, creation_time DESC)
但是以下查询的结果告诉我type
是range
,它会扫描表格中901行中的100行,而extra
是using index condition
。不应该只是ref
,即转到索引,从中获取第一项,返回?