nested subquery

the results we need. However, we can also write: select customer_id, order_id from table2 where customer_id in (select customer_id from table1 where city='hangzhou'); ER? What is the select statement in brackets? The question is, what is the syntax and how the task can be completed, so this blog will focus on this issue.What is a subquery? In short, the subquery is: As shown in, subqueries are called in

Basic knowledge1, associated subqueries and unrelated subqueries In a unassociated subquery, an internal query executes only once and returns its value to an external query, and the external query uses the value returned to it by the internal query in its processing. In the associated subquery, the internal query is executed once for each row of data returned by the external query. In addition, the informa

A subquery is the embedding of a SQL Sever statement into another SQL Sever statement. The database engine performs a query operation on a subquery as a virtual table. Subqueries can be used as a table in a join statement, either as a value in a SELECT statement, as a SQL sever query clause, or as a phrase in a SQL sever query clause, mixed with a data manipulation statement. The execution of a

| +------+--------+------+------+------+-----------+--------------+ 1 row in Set (0.00 sec) mysql> Example: Querying employee and Department tables using an inner join and displaying query results in ascending order of the age field mysql> mysql> Select Num,name,employee.d_id,age,sex,d_name,function-From employee,department where employee.d_id=department.d_id , order by age ASC; +------+--------+------+------+------+-----------+--------------+ | num | name | d_id | age | sex

Tags: repeat avghighlight other -- ddlcomm How to use process A subquery actually refers to a SELECT statement that is embedded in another statement, also known as a nested query. It is worth noting that subqueries can use the ORDER BY clause when a subquery is applied in a DDL statement. 　　However, in a WHERE clause in a DML statement, a

Ask! When mysql returns a fixed result set, whether the result set is repeatedly executed, for example, 1: selectt. *, (selectcount (1) fromtable01) fromtable01t; for example, 2: selectt. *, (selectcount (1) fromtable01t2wheret2. keyt1.key) fromtable01t1; -- Nested subqueries like this will be executed repeatedly. Q: In the subquery traversal process in example 1 above, there are fixed result sets. Will the

I. Basic usage of sub-selection1. Definition of sub-selectionChild iterations allow one query to be nested in another query. For example, an exam score item divides exam events into two types: exam (T) and quiz (Q. The following query only shows the students' test scores.Select * from score where event_id in (select event_id from event where type = 'T ');2. Sub-selection usage (3)Generate a reference value using sub-selection.In this case, an internal

(select 1 from emp e where e.deptno = D.deptno);--in and Null valuesSql>SELECT *From EMP EWHERE E.empno not in (SELECT 7369From dualUNION AllSELECT NULL from dual);Sql>SELECT * from emp e WHERE e.empno in (' 7369 ', NULL);Note: Subqueries are included in parenthesesSubqueries are generally placed on the right side of the comparison criteria do not use ORDER by in a subquery unless you perform a top-n analysis. Eight, Dolez query1. Comparison of paire

Inquire:In a select query, another select query is nested. One is the outer query and the other is the inner query.where child query That is, the WHERE query statement has a SELECT statement that treats the results of the inner query as the condition of the outer query. From child query In the FROM query statement, there is a SELECT statement that takes the inner query result as a temporary table for the outer layer to query again. Difference: Fo

SQL is required. note Chapter 1 use subquery. SQL is required.11.1 subquery Query any SQL statement is a query. However, this term generally refers to a SELECT statement.SQL also allows you to create subqueries, that is, queries nested in other queries.11.2 Filter Using subqueries SELECT cust_idFROM OrdersWHERE order_num IN (SELECT order_num FROM OrderItems WHE

We all know that we can use Oracle subqueries in HAVING, and the results of the two query statements can be used for set operations. If you want to know how we use Oracle subqueries in HAVING? And how can the results of the two query statements perform the actual operations on the set? The following are related answers. 1. the query statement can be nested. Example: SELECT ...... FROM (SELECT ...... FROM table name 1, [Table name 2,...] WHERE conditi

Case Combing time: 2013-9-25 written in the previous words: In slow-scan optimization 1 and 2 have repeatedly emphasized the importance of explain, but sometimes the naked eye can not see how the explain Results to guide optimization, this time also need some other basic knowledge of the support, and even need to understand the MySQL implementation principle, such as sub-query slow-scan optimization . When you see the "DEPENDENT subquery