mysql - Using SQL EXPLAIN to gain information about a query -


i'm looking @ 2 queries i've finished, , i'm trying decide 1 should implement. main difference between 2 sql explain select_type. query #1 select_type 3 rows simple. query #2 primary. else same except possible keys in query #2. question are...

  1. what difference between simple , primary , there other select_type's
  2. which select_type should try accomplish majority of queries performance standpoint (guessing answer depends i'll ask anyway)
  3. any other pointers on how use explain gain valuable data query , decide take there


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