subquery vs join performance mysql

| DEPENDENT subquery | Film_actor | Eq_ref | primary,idx_fk_film_id | +----+--------------------+------------+--------+------------------------+ Depending on the output of the explain, MySQL will scan the full table for film tables and perform subqueries on each row found, which is a bad performance. Fortunately, it's easy to rewrite it as a

follow the join condition after ON, and write the conditions for the central table to the WHERE clause.Statement 9: FULL OUTER JOIN ).Select o. ID, O. ORDER_NUMBER, O. CUSTOMER_ID, C. ID, C. NAMEFrom orders o full outer join mers c on c. ID = O. CUSTOMER_ID;Note: MySQL does not support all external connections. the me

such statements is to split them into two query statements. If you do not want to split them into two independent queries, you can also join the query with the temporary table ,: If you do not want to split it into two independent queries, you can also join the temporary table for query, as shown in the following optimized SQL: SELECT g1.gid, count (1) FROM shop_goods g1, (select gid from shop_goods WHER

SQL Optimization-logical Optimization-subquery optimization (MySQL) and sqlmysql 1) subquery concept:When a query is a subquery of another query, it is called a subquery (a query statement is nested in the query statement ). Subqueries are located: A) Target column posi

table ,: If you do not want to split it into two independent queries, you can also join the temporary table for query, as shown in the following optimized SQL: SELECT g1.gid, count (1) FROM shop_goods g1, (select gid from shop_goods WHERE sid in (latency, 1466110,1466102, latency) g2 where g1.status = 0 and g1.gid = g2.gid group by g1.gid; I checked it with explain, and now I have a new keyword "DERIVED", which is used for subqueries IN THE from clau

where phone = ' 82306839 ';+----+-------------+-------+------+-----------------+-----------+---------+-----------------+------+----------- ---------------+| ID | Select_type | Table | Type | Possible_keys | Key | Key_len | Ref | Rows | Extra |+----+-------------+-------+------+-----------------+-----------+---------+-----------------+------+----------- ---------------+| 1 | Simple | B | Ref | phone,number_id | Phone | 66 |Const | 6 | Using where; Using Index || 1 | Simple | A | Ref | number_id

This article introduces four database query methods by combining text and text: Basic query, connection query, subquery, and regular expression query, for more information, see query data to obtain the required data from the database. Data query is the most common and important operation in database operations. You can use different query methods based on your data requirements. You can obtain different data through different query methods.

of subqueries. For more explanation of explain, please refer to here.Related subqueries A correlated subquery refers to a subquery that references an external query column, that is, a subquery evaluates each row of the outer query. But within MySQL, dynamic optimizations can be made differently depending on the situ

MySQl subquery, left-right join, and multi-table join learning Notes 1. subquery refers to the SELECT clause in another query statement. Example: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2 ); SELECT * FROM t1... is called Outer Query [external Query] (or Oute

Mysql Query, subquery, and connection query analysis: bitsCN.com I. five clauses of mysql Query: where (conditional query), having (filter), group by (group), order by (SORT), Limit (limit the number of results) 1. Common where operators: comparison operators >,Goods group by cat_id; good_name in the result obtained here is incorrect! Because shop_price uses the

1. what is subquery and table join query? subquery: The select query statement is used in the select or where clause of the primary SQL statement; selectaname, (selectbnamefrombwherebidaid) fromawhereanamelika % table off 1. what is subquery and table join query: