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Re: MYSQL5.7:OPTIMIZER Contradict Explain
Posted by: yijie fu
Date: September 07, 2022 05:26AM

key_len (JSON name: key_length)

The key_len column indicates the length of the key that MySQL decided to use. The value of key_len enables you to determine how many parts of a multiple-part key MySQL actually uses. If the key column says NULL, the key_len column also says NULL.

Due to the key storage format, the key length is one greater for a column that can be NULL than for a NOT NULL column.


This explanation may have some ambiguities´╝înot The key_len column indicates the length of the key that MySQL decided to use. Memory alignment may not be included? i cant understand it.

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September 07, 2022 05:02AM
Re: MYSQL5.7:OPTIMIZER Contradict Explain
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