db2 subquery

1. Self-query refers to multiple small queries embedded in a complete query. According to different requirements, self-query can appear in any position of the query statement, but in from, where and having clauses are followed by many cases.2. The results returned by the self-query are divided into four types: single-row Single-Column subquery, single-row multi-column subquery, multi-row Single-Column

Basic query optimization and subquery Optimization in Oracle databases 1. Reasonably sort query Conditions Oracle uses the bottom-up sequence to parse WHERE data. From the perspective of performance optimization, we recommend that you write the conditions that can filter out a large number of record rows at the end of the WHERE clause and The join conditions between them are placed before other WHERE clauses, that is, the conditions that are easy to t

Mysql common query: groupby, left join, subquery, havingwhere I went to two relatively popular Internet companies for an interview a few days ago. I encountered a problem in SQL, first, let's take a brief look at score1 and groupby in the two-dimensional table for grouping by a certain dimension. For example: calculate the total score of each student, SELECTstudent, SUM ( Mysql commonly used query: group by, left join,

Put the entire folder (jmam_dq.0) to D:\db_bak\Start-run, enter Db2cmd:1. Create a databaseDB2 Create DB dbname on D:(The database in the D disk, then the system will automatically add sql0000* directory, the result directory such as: D:\db2\node0000\sql0000*\ ...;If the remote connection database is created, perform DB2 attach to Servernode user ... using ... before you perform the create. )2. Restoring th

statements. Chapter 3rd describes the SQL standards and principles to be followed in writing high-quality SQL statements. Chapter 4th describes SQL program queries; chapter 5th describes how to check the existence with two instances; Chapter 6th describes runstats for some statistical information; Chapter 7th describes the "15-step tuning method" for DB2 performance optimization ", it is known as the invaluable benefit of the

Original address:Http://hi.baidu.com/wader2006/blog/item/78406b60b51f8b47ebf8f8f0.htmlDB2 Common Command Set----DB2 maintenance 2007-09-09 10:10 in the DB2 development process, the whole development process also has a very important part of the work is the maintenance of the database, for the maintenance of a huge information system is very necessary; Leave a simple maintenance manual for a rainy night. Som

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 WHERE prod_id = 'rga01 '); In SELECT statements

MySQL database BASICS (4) (subquery and link) (in continuous update), mysql is being updated 1. subquery Introduction The so-called "outer Query" does not refer to "Search", but is the collective name of all SQL statements. The Structured Query Language (Structured Query Language) is short for SQL. : 2. subqueries caused by comparison Operators Note: When a

1. PhenomenaCREATE Table A as (select 1 as col_a), create table B as (select 2 as Col_b) SELECT * from a Where col_a in (select Col_a fro M b)Where Col_a exists only in table_a, Table_b does not have the field, and the result of the entire statement can be executed successfully!2. Reason:The problem is confusing, and the reason for this is that "automatically looks for the outer layer when the column name in the subquery does not exist."In other words

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 result be repeated for N times (N records )?

Where subquery failed. This post was last edited by u010572351 from 2013-06-2817: 14: 25 nbsp; select nbsp; goods_id, cat_id, nbsp; goods_name nbsp; from nbsp; goods nbsp; where where subquery aborted, This post was last edited by u010572351 at 17:14:25 Select goods_id, cat_id, goods_name from goods where goods_id = (Select max (goods_id) from goods ); The statement is correct! However: Query the

Where subquery failed. This post was last edited by u010572351 from 2013-06-2817: 14: 25 nbsp; select nbsp; goods_id, cat_id, nbsp; goods_name nbsp; from nbsp; goods nbsp; where nbsp; goods_id nbsp; (select where subquery failed, This post was last edited by u010572351 at 17:14:25 Select goods_id, cat_id, goods_name from goods where goods_id = (Select max (goods_id) from goods ); The statement i

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 condition) WHERE condition 2; 2. Where can I use Or

where stu_id in (select stu_id from GRADE where stu_score>85); Find student information that is greater than 85 points 2. Combined with existsThe exists and not EXISTS operators only test whether a subquery returns rows of data. If yes, exists will be true,not exists will be false. SELECT * from STUDENT where EXISTS (select stu_id from GRADE where stu_score>=100); If you have a student score greater than 100, ju

First, group queryUse the group BY keyword to group data, use the HAVING keyword to set constraints on grouped data, and complete data grouping and statistics1.1 Aggregation functions: Often used to achieve data statistics functions①count () Statistics record number of records②sum () sum③min () to find the minimum value④max () to find the maximum value⑤avg () averagingExample: Query the average worker number for all employeesNote: The SELECT statement queries only one value, so you cannot use li

Mysql exists subquery can be divided into: from where and exists subquery www.2cto.com classification table: [SQL] mysql> select * from category; + ---- + --------- + | id | c_name | + ---- + --------- + | 1 | ios | 2 | android | 3 | sb | + ---- + --------- + 3 rows in set item table: www.2cto.com [SQL] mysql> select * from goods; + ---- + --------- + -------- + ------- + | id | name | cat_id | price | num

I went to an interview with two cool Internet companies a few days ago and encountered problems in SQL. Well, unfortunately, let's take a look at it. Score 1. Use group Group by Dimension For example: Calculate the total score of each student. SELECT student, SUM (score) FROM score group by student Average score for each student SELECT student, AVG (score) FROM score group by student You can also follow the class and Course2. Differences between having and where: having is similar to wh

Introduction to the use of with in oracle subquery; Introduction to oracle Recently I have studied oracle and want to improve the efficiency and ease of reading of statements I have written. Today's note is about subquery factors. Factor-based query may not necessarily improve efficiency, but it will certainly improve the readability of the program. -- With statement with sales_c (select sales, e_NO, e

I collected online materials and added my own SQL. 1. Group by is a group query. Generally, group by isUsed with aggregate Functions The principle of group by is that all columns after select do not use aggregate functions and must appear after group. 2. Having The where clause is used inBefore grouping query resultsRemove rows that do not meet the where condition, that is, filter data before grouping,The condition cannot contain clustering functions., Use the where ConditionShow specifi

Mysql Database SQL Optimization-subquery optimization and mysql Database SQL Optimization1. What are subqueries and table join queries:Subquery: The select statement is used in the select or where clause of the primary SQL statement; select. name, (select B. name from B where B. id =. id) from a where. name lik 'a %'Table join query: a joint query of multiple tables; select. name, B. name from a, B where. id = B. id and. name like 'a % ';Although the