Adding unique index check for schema_unused_indexes

[ggunson]

Currently the schema_unused_indexes view will return unique (non-primary) indexes if they are unused. This could be because the server has been recently restarted, or there haven't been any writes to the table since the last restart.

This PR modifies the schema_unused_indexes view definition to filter out unique indexes. This is done via a join on information_schema.statistics, making the new select:

SELECT t.object_schema,
       t.object_name,
       t.index_name
  FROM performance_schema.table_io_waits_summary_by_index_usage t
 INNER JOIN information_schema.statistics s 
    ON t.object_schema = s.table_schema 
   AND t.object_name = s.table_name 
   AND t.index_name = s.index_name
 WHERE t.index_name IS NOT NULL
   AND t.count_star = 0
   AND t.object_schema != 'mysql'
   AND t.index_name != 'PRIMARY'
   AND s.NON_UNIQUE = 1
   AND s.SEQ_IN_INDEX = 1
 ORDER BY object_schema, object_name;

Since there's one row for each column in an index in the statistics table, I have it join on only the first column's row (s.SEQ_IN_INDEX = 1).

The join is on an information_schema table, and the view definition is under the p_s heading, so I don't know if this join changes that categorization.

Note this change will also require a modification of the help docs.

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[mysql-oca-bot]

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[mysql-admin]

Sorry for the confusion - this was closed prematurely
==Omer

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[ggunson]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

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bug http://bugs.mysql.com/bug.php?id=83257 for updates.
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