SQL and Ado notes

Side translation: Script

SQL is a standard that works in conjunction with database programs language , these database programs include MS Access ,DB2 ,Informix ,MS SQL Server ,Oracle ,MySQL ,Sybase and so on.

1. SQL function statements (with many built-in functions) plus SQL conditional statements.

2. 2. aggregate functions, such as SUM, often require the addition of a GROUP by statement.

GROUP by Statement

GROUP by statements are used in conjunction with aggregate functions to group result sets based on one or more columns.

SQL GROUP by Grammar

SELECT column_name, aggregate_function (column_name)

From table_name

where column_name (column) operator (operator) value (value)//(WHERE clause) where column operator values

。

GROUP by column_name// group the results.

SQL uses single quotation marks to wrap text values (most database systems also accept double quotes). If it is a numeric value , do not use quotation marks.

Text value:

That's right:

SELECT * from Persons WHERE firstname= ' Bush '

This is wrong:

SELECT * from Persons WHERE Firstname=bush

Numerical:

That's right:

SELECT * from Persons WHERE year>1965

This is wrong:

 select * from persons where year> ' 1965 ' 
 

In addition to numbers without quotes, the other add    quote WHERE clauses combine  AND  and  OR  operators we can also put  AND  and  OR  Combine (use parentheses to form complex expressions):select * from persons where  (firstname= ' Thomas '  OR  Firstname= ' William ') and lastname= ' Carter '   sql View considerations: 1. In  SQL , the view is based on  SQL  A visual table of the result set of the statement. 2. The view contains rows and columns, just like a real table. A field in a view is a field from a real table in one or more databases. We can add  SQL  functions, where , and  JOIN  statements to the view, and we can also submit the data as if it came from a single table. Note: The design and structure of a database is not affected by functions, where , or  join  statements in the view. Note: Views always display the most recent data. Each time a user queries the view, the database engine rebuilds the data by using the  SQL  statement. Syntax Example: create view [current product list] (depending on the chart name)  asselect productid, ProductName (column name) from products  (table name) where discontinued=no (conditional) ado  objects have two types of properties: Built-in and dynamic. Built-in properties are properties that are implemented in  ADO  and immediately available to any new object, using the myobject.property  syntax. They do not appear in the  Properties  collection of objects as  Property  objects, so although you can change their values, you cannot change their properties. The ado property  object represents the dynamic nature of the  ADO  object, and the dynamic property is  proviDefined by the der . Each  provider  has a different way to interact with  ADO  in the  ADO  dialog. So,ado  need some way to store information about  provider . The workaround is to  provider  provide specific information (dynamic properties) for  ADO . ado  stores each  provider  attribute in a  Property  object, and the  Property  object is stored accordingly in the  properties   in the collection. This collection is assigned to the  Command  object, the connection  object, the field  object  , or the  Recordset  object. For example, a property assigned to a provider might indicate whether the  Recordset  object supports transactions or updates. These additional properties appear as  Property  objects in the  Properties  collection of the  Recordset  object.  ADO  each object. Command (simple query)       connection (and Database link)  error (collect error message)    field ( Corresponds to a column)     parameter (provides parameter information)   property (dynamic property)  record (accommodates a file/record/information)   Recordset (holds recordset)  stream (handles binary data or text flow)  MVC  (model model  view View  controller control)   The efficient lightweight visual studio express  is a development tool tailored for  MVC  (and  web forms). mvc  is a box for building  web  applicationsRacks, using  MVC  (Model view controller)   Design: Model represents the core of the application (such as a list of database records) view (view) displays data (database records) to display the controller (Controller) to process input (write database records) mvc  model also provides the  html, Full control of CSS and  JavaScript . The mvc  model defines  web  applications through three logical tiers: business     layer (business layer, model logic) display  Layer (display layer, view logic) Input control (input control, controller logic)    xml is also a markup language  1. Independent ability to troubleshoot log location issues

SQL and Ado notes