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Sql to develop good writing habits

We do software development, most people can not do without dealing with databases, especially erp development, dealing with the database more frequently, every turn is thousands of lines of stored procedure, if the data volume, the movement of large,

oracle's CONNECT BY and START WITH

Used in the SELECT command CONNECT BY and START WITH clause can query the tree structure table in the relationship. The command format is as follows: SELECT ... .. CONNECT BY {PRIOR = column names column names 1 2 | 1 = PRIOR column name column name

Detailed examples of El expression Yong video (reproduced)

Original link: http://suo.iteye.com/blog/407690 Of the JSTL EL expressions to do in the next test (the specific process can be found in Shang Xuetang video) Step 1: Add JstlElAction class Java code package com.bjsxt.struts; / ** * EL expression test

To develop a good habit to bring a big SQL wealth

This article comes from: http://database.51cto.com/art/201105/265497.htm We do software development, most people can not do without dealing with the database, in particular, erp development, dealing with the database more frequently, every turn is th

Oracle was Nvl function

Oracle was Nvl function (2006-11-02 22:38) Category: Oracle nvl () function, for example, see from the two expressions return a non-null value. Grammar NVL (eExpression1, eExpression2) Parameter eExpression1, eExpression2 If eExpression1 evaluates to

Index Tuning turn ___MySQL Order By

MySQL Order By Index Tuning In some cases, MySQL can use indexes to satisfy an ORDER BY or GROUP BY clause without doing extra sorting. Although the ORDER BY is not an exact match and the order of the index, the index can still be used, as long as th

Principles of good practice and perform SQL

Principles of good practice and perform SQL I: the logic of the query execution order (1) FROM (2) ON (3) JOIN (4) WHERE (5) GROUP BY (6) WITH {cube | rollup} (7) HAVING (8) SELECT (9) DISTINCT (11) (10) ORDER BY Standard SQL parsing order: (1). FROM

SQL Server 2005 to simplify the use of synonyms development

Turn I. Introduction If you have any development using SQL Server software, then you will definitely use the four-part identifiers are used to refer to an object: [[[Server.] [Database].] [Schema_name].] Object_name As shown above in square brackets,

introduction and use sp_executesql

sp_executesql Implementation can be reused many times or dynamically generated Transact-SQL statement or batch. Transact-SQL statement or batch can contain embedded parameters. Grammar sp_executesql [@stmt =] stmt [ {, [@params =] N'@parameter_name d

Aggregate functions and grouping [turn]

Note that count (*) and count (column name) difference between the usage of Using the count (column name) when a column a null value when, count (*) will still be calculated, but the count (column name) does not Using the count (distinct column names

oracle view and its function

----------- DBA_ DBA_2PC_NEIGHBORS connection with pending transactions to enter and exit the connection information. DBA_2PC_PENDING includes distributed transactions awaiting recovery information. DBA_ALL_TABLES display all tables in the database (

NEXTVAL and CURRVAL operator

You can use the SQL statement or CURRVAL NEXTVAL operator to access the sequence values. Sequence.CURRVAL format must be used sequence.NEXTVAL or reside in the same sequence in the database name (or synonyms) to qualify NEXTVAL or CURRVAL. Expression

the oracle nvl () function

The usage of oracle nvl function Obtained by querying the total value of a field, null if this value will give a bit preset default values select nvl (sum (t.dwxhl), 1) from tb_jhde t where zydm =- 1 Concern here nvl usage, nvl (arg, value) means tha

group by.order by.where.distinct Use Summary

One. Group by 1.GROUP BY WHERE clause used for the results obtained in the group, which means it is executed after the WHERE clause of WHERE filtered through some of the columns are grouped according to the results, after appropriate processing . Note: If

ORA-00937: not a single-group group function solution

A SELECT list cannot include both a group function, such as AVG, COUNT, MAX, MIN, SUM, STDDEV, or VARIANCE, and an individual column expression, unless the individual column expression is included in a GROUP BY clause. Drop either the group function

MySql queries related issues

A.5. And Query-Related Issues A.5.1. Search Case Sensitivity A.5.2. Using DATE Columns problems A.5.3. The problem with NULL Values A.5.4. The problem with Column Aliases A.5.5. Rollback Failure for Non-Transactional Tables A.5.6. Deleting Rows from Relat

Good writing habits and knowledge of SQL (SqlServer for example)

We do software development, most people can not do without dealing with the database, in particular, erp development, dealing with the database more frequently, every turn is thousands of lines of stored procedures, if the data volume, the movement o

oracle stored procedure tuning Basics

1, use other libraries if the Table or View, be sure to create a View in the current library to implement cross-database, it is best not to use "databsevv.dbo.table_name", because it can not show that the SP sp_depends used cross-library ta

Basic database CRUD statements

adoquery1.Fielddefs [1]. Name; field name dbgrid1.columns [0]. width: = 10; dbgrid field width adoquery1.Fields [i]. DataType = ftString field type update jb_spzl set kp_item_name = upper (kp_item_name) to modify a database table as the upper select

Why Oracle will sometimes use the index to find data? - To force Oracle to use the best "implementation plan"

[Abstract] you use the SQL language, a query to the database release, Oracle will have with an "implementation plan", that is what the statement by the data search program execution. Search program selection is closely related to the Oracle opti

Oracle: oracle sum (sum) count (number) of the difference

In the development, we often encounter a "total (count)" or "accumulate (sum)" as a condition of the query. Such as aaa table: ID, NAME, SHU 1, a, 3 2, a, 4 3, b, 5 4, b, 7 5, a, 6, a, 20 Example 1: Query appeared twice name. Beginners

About Group By statement (SQL syntax)

1. Group By statement Description: Group By statement from English to understand the literal meaning is "according to (by) the rules must be grouped (Group)". Its role is to rule a certain data set is divided into several small areas, then

Oracle uses the sum (collection at Forum)

One. Oracle database data types commonly used varchar2 (length) variable length strings char (length) length number () indicates the integer or floating-point number (8) number (8,2) clog character large object blog binary large object II. Database query

SqlServer in decimal (numeric). Float and real data types difference

http://blog.csdn.net/zwxrain/archive/2009/03/20/4006431.aspx decimal data type can store up to 38 numbers, all numbers are able to put the right of the decimal point. decimal data type stores an accurate (exact) number of expressions; approximations

SELECT Clause Ordering

Clause Description Required SELECT Columns or expressions to be returned Yes FROM Table to retrieve data from Only if selecting data from a table WHERE Row-level filtering No GROUP BY Group specification Only if calculating aggregates by group HAVING

Grouping and Sorting

ORDER BY GROUP BY Sorts generated output. Groups rows. The output might not be in group order, however. Any columns (even columns not selected) may be used. Only selected columns or expressions columns may be used, and every selected column expressio

SQL Select statement is a complete implementation of the order:

SQL Select statement is a complete implementation of the order: 1, from clause assemble data from different data sources; 2, where clause based on specified criteria to filter the rows of records; 3, group by clause divides the data into multiple pac

MySQL statement optimization principle

1, using the index to quickly traverse the table. By default non-clustered index created index, but sometimes it is not the best. In the non-clustered index, the data is physically stored in random data page. Rational index design should be based on

Select statement execution order

Select the purpose is to understand how [Search] from: Standard SQL parsing order: (1). FROM clause, assembling data from different data sources (2). WHERE clause, based on specified criteria to filter records (3). GROUP BY clause, the data is divide

Turn --- Oracle review

One. Oracle database data types commonly used varchar2 (length) variable length strings char (length) length number () indicates the integer or floating-point number (8) number (8,2) clog character large object blog binary large object II. Database query

Materialized view query rewrite constraints [Reserved]

Materialized view is an important feature is support for query rewrite. If the initialization parameter query_rewrite_enabled set to TRUE, and the CBO, when issuing the query on the base table, Oracle will automatically determine whether the use of t

To grasp the Oracle database cursor to use

Explicit Cursor When the query returns results more than one line, you need an explicit cursor, then the user can not use select into statement. PL / SQL managing implicit cursor, when the query began to open when the implicit cursor, implicit cursor

mysql syntax entry 3

7.4.13 used in conjunction with GROUP BY clause function If you do not include a statement GROUP BY clause to use an aggregate function, which is equivalent to the aggregate of all lines. COUNT(expr) Return statement by a SELECT rows retrieved the nu

Databases are often used statements

SQL common commands to use: (1) data record selection: sql = "select * from table where field name = field value order by field name [desc]" sql = "select * from table where field names like '% field value%' order by field name

For the result set using union and the principle of

1, union must have two or more combinations of select statements, each with a union between separate select statement. 2, each select statement to select between where the content must be the same, that they must contain the same columns, expressions

oracle writing experience (rpm)

This Transfer: http://bbs.chinabyte.com/thread-381770-1-1.html The following article is written for Oracle stored procedure experience and optimization of specific operations, if you are related to the actual operation of their interest, you can clic

Decode using Oracle's multi-function value to determine

decode function more expressions and search words, if the match result is returned; if you do not match, return default value; If no default value, null value is returned. The following is a simple test, used to describe the Decode function is used:

Common database conversion statement

The following is management access SQL functions, a function of differences in the databases due to different Sql database functions of its different here with the function encapsulates the differences: / ** * Instr character replacement script (colu

oracle in the view of learning

[/ Size] [size = x-large] [/ size] [size = xx-large] [align = center] [/ align] After a customized view to display is included in one or more tables (or other view) data. view the output for the query, and as the table to deal with, so you can view a

Switch to a an article on optimizing sql

We are in discussions on database optimization stuff, just involved in the development of a data warehousing project, the following things be a little database optimization study + combat some of the feelings and experiences, and come up with to shar

SQL table constraints

Constraints limit the data type is what we can store data in a table way. However, for many applications, this restriction is too rough. For example, a price field should contain only accept positive numbers. But no kind of standard data type accepts

Basic use of SQL, AS

Retrieve data from a table is the query the table. SQL SELECT statement to do this is to use. The statement is divided into a select list (list to return to the field), the table lists (lists of data retrieved from the table), and optional conditions

How MySQL Uses Indexes

How MySQL Uses Indexes Some used to quickly locate a specific index value records. If there is no index, MySQL must begin from the first row to read the entire table to retrieve the records. Larger the table, the greater the consumption of resources.

study notes oracle four (subquery)

Subquery: Check the names of employees the highest wages select ename, sal from emp where sal = (select max (sal) from emp); Query wages higher than the average wage of employee information select ename, sal from emp where sal> (select avg (sal) f

oracle case when then determine the conditions

select (case when 1 = 1 then 1 else 2 end) from dual; select (Case when (6-4) = 1 then 1 when (6-5) = 2 then 2 else 2 end) from dual; select decode (3-1,2,1,3) from dual; Expressions 3-1, if the return value of 1 equals 2, otherwise 3

SQL Tuning Optimization

Original address http://blog.csdn.net/zhaoer8270/archive/2008/09/17/2942790.aspx 1, using the index to quickly traverse the table. By default non-clustered index created index, but sometimes it is not the best. In the non-clustered index, the data is

oracle COALESCE function resolution

COALESCE Returns its argument in the first non-empty expression. Grammar COALESCE (expression [, ... n]) Parameter expression Any type of expression. n You can specify multiple expressions that placeholder. All expressions must be the same type, or c

Have time to see what oracle-review summary (rpm)

One. Oracle database data types commonly used varchar2 (length) variable length strings char (length) length number () indicates the integer or floating-point number (8) number (8,2) clog character large object blog binary large object II. Database q

What database constraints? Three paradigms

What database constraints? Database constraints is to standardize data and ensure data integrity of a high limit. Common database constraints are: 1. Check constraints Check constraints that check constraints, set the property by forcing the field to

sql statement optimization principles with millions of data optimization

1, using the index to quickly traverse the table. By default non-clustered index created index, but sometimes it is not the best. In the non-clustered index, the data is physically stored in random data page. Rational index design should be based on
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