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23 lines
1.8 KiB
SQL
23 lines
1.8 KiB
SQL
explain select *,
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(select count(*) from sakila.film as outer_sub where outer_sub.film_id = outer_der.film_id)
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from (
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select *,
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(select count(*) from sakila.film as mid_sub where mid_sub.film_id = mid_der.film_id)
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from (
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select *,
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(select count(*) from sakila.film as inner_sub where inner_sub.film_id = inner_der.film_id)
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from sakila.film as inner_der
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) as mid_der
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) as outer_der;
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+----+--------------------+------------+--------+---------------+---------+---------+-------------------+------+--------------------------+
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| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
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+----+--------------------+------------+--------+---------------+---------+---------+-------------------+------+--------------------------+
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| 1 | PRIMARY | <derived3> | ALL | NULL | NULL | NULL | NULL | 1000 | |
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| 3 | DERIVED | <derived5> | ALL | NULL | NULL | NULL | NULL | 1000 | |
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| 5 | DERIVED | inner_der | ALL | NULL | NULL | NULL | NULL | 951 | |
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| 6 | DEPENDENT SUBQUERY | inner_sub | eq_ref | PRIMARY | PRIMARY | 2 | inner_der.film_id | 1 | Using where; Using index |
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| 4 | DEPENDENT SUBQUERY | mid_sub | eq_ref | PRIMARY | PRIMARY | 2 | mid_der.film_id | 1 | Using where; Using index |
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| 2 | DEPENDENT SUBQUERY | outer_sub | eq_ref | PRIMARY | PRIMARY | 2 | outer_der.film_id | 1 | Using where; Using index |
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+----+--------------------+------------+--------+---------------+---------+---------+-------------------+------+--------------------------+
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