subquery vs join performance mysql

mapply.mid = Mconfig.mid WHERE Mapply.aid In ( SELECT Aid From ' mapply ' where state = $state ORDER BY ' atime ', ' uid ' DESC ) So no error, MO away thought OK, but after running found that the data have problems and simply read out the content of the application form is not the same, only to find limit position misplaced, and then put limit in, the results of the following error This version of the MySQL doesn ' t yet support

Generally, the most basic paging method of MySQL is as follows: Select * from content order by id desc limit 0, 10 In the case of small data volumes, such SQL statements are enough. The only problem that needs to be paid attention is that indexes are used. As the amount of data increases, the number of pages will increase. The SQL statements on the last few pages may be similar: Select * from content order by id desc limit 10000, 10 In a word, the

This example describes the MySQL subquery usage. Share to everyone for your reference, specific as follows: Suppose the table my_tbl contains three field a,b,c; now you need to query the number of records for which column B is the minimum for each different value of column A in the table. For example, the table record is: A b C1 3 ' CD '2 3 ' nHD '1 5 ' BG '2 6 ' CDs '1 7 ' Kiy '3 7 ' VSD '3 8 ' NDF ' E

[Mysql] An example of subquery assumes that the table my_tbl contains three fields a, B, and c; now we need to query the minimum value of Column B under each different value of column a in the table. For example, the table record is: a B c1 3 'cd' 2 3 'nhd' 1 5 'bg '2 6 'cd' 1 7'kiy' 3 7'bf'3 8'ndf' expected results is: a B c1 3 'cd' 2 3 'nhd '3 7' _ (1) One of the practices is to first find the minimum val

DBAs or developers who have used Oracle or other relational databases have the experience of thinking that the database has been optimized for the subquery, that it is a good choice to drive the execution of the table, and then porting that experience to the MySQL database, but unfortunately, MySQL may disappoint you in the processing of subqueries, as we encount

Tdb_goods_types as P left joins Tdb_goods_types as s on s.parent_id = P.type_ Id --Find the number of all categories and their subclasses SELECT P.type_id,p.type_name,count (s.type_name) as Children_count from Tdb_goods_types as P left JOIN Tdb_goods_types as s on s.parent_id = p.type_id GROUP by P.type_name ORDER by p.type_id; --Add Child_count field for Tdb_goods_types ALTER TABLE tdb_goods_types ADD child_count mediumint UNSIGNED not NULL DEFAULT

, when we create the index at this time left JOIN .... Is IsNull execution time is more than twice times that of not exisits. To this, about the left JOIN ... Is null and not exists to this end, I need the same next basic conclusion. Left JOIN ... Is null and not EXISTS performance Analysis conclusion: when we need to

;=" .- .- on xx:xx:xx" andPay_time" .- --Geneva A: -: -"Group bypay_id having Count(pay_id)> 1 ); Execution result: 2.23 seconds The second way of writing, and the sub-query to join association, this is equivalent to the above in the subquery writing, the following test found that the efficiency is indeed a lot of improvement SelectTpp1.* fromtest_table2 Tpp1, (Selectpay_id fromTest_table2WHEREPay_time

Mysql-join query, mysql-joinThree methods of MySQL association query: SELECT * FROM film JOIN film_actor ON (film. film_id = film_actor.film_id );SELECT * FROM film JOIN film_actor USING (film_id); -- when the field names of the

right 2 tables + no matching record in table (left field null)Syntax: Select column 1, column 2, column 3, ...From table 1Right join table 2 on table 1. column x = table 2. Column YFull Link: Cartesian product cross join for records in left and right 2 tablesSyntax: Select column 1, column 2, column 3, ...From table 1Cross Join Table 2V. LIMITSyntax: limit [m,]n

execution is a lot more efficient, and you don't need to scan 5.71 million records, it takes only 0.01 seconds to execute. Query OK, 5 rows affected (0.01 sec) 3. Other suggestions Although the version of MySQL 5.6 and above is optimized for subqueries, the results of this case are not satisfactory in some cases. Therefore, if you find that some subquery SQL is less efficient, you can try to rewrite t

Tags: Employees customer number Tom CTE order by using sales Mysmysql-Sub-queryA MySQL subquery is a query that is nested within another query. MySQL subqueries can also be nested within another subquery. A MySQL subquery is calle

Label:Reference article: SQL Server Performance Tuning Overview (good summary, don't miss it.)Database: System Database Usage of subqueries A subquery is a select query that is nested within a SELECT, INSERT, UPDATE, DELETE statement, or other subquery. Subqueries can be used anywhere that an expression is allowed to be used. Subqueries can make our programming f