So whenever I EXPLAIN my query, I often get instances in which it states certain fields as possible keys but then the key table will be null…
Why would MySQL do this and decide to use no keys when in fact it can use a possible key?
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So whenever I EXPLAIN my query, I often get instances in which it states certain fields as possible keys but then the key table will be null…
Why would MySQL do this and decide to use no keys when in fact it can use a possible key?
It can’t always use a key, for instance:
Although
idis a possible key for both lookups, it can’t be used for both. One of the tables must do a full scan.