Basic knowledge of the database

Source: Internet
Author: User
Tags one table

Almost all business applications need to process a large amount of data and organize it into a format that is easy to read. This requirement can usually be implemented through the database management system (MDBs). MDBs is the mechanism for manipulating tabular data with advanced commands. The database management system hides the low-level details of how data is stored in the database, allowing programmers to focus on managing information, rather than taking into account the specific operations of files or the maintenance of data connection relationships.
Here are a few basic concepts to start with.
Database: A database is a set of related information that is arranged to be easily processed or read. The actual data in the database is stored as a table (table), similar to random access to the file. The data in a table consists of rows (row) and column (column) elements that contain the same block of information that has the same structure, similar to random access to records in a file, or a set of values (or a collection of fields), as shown in Figure 1:

Figure 1: Graphical representation of the database and table structure

Recordset: a Recordset (Recordset) is multiple objects that represent a collection of objects in one or several tables. In database programming, the recordset equals the variables in the program. Tables in the database do not allow direct access, but can only be browsed and manipulated through the Recordset object. A recordset is composed of rows and columns, similar to tables, but can contain data from multiple tables. The contents of the grid shown in Figure 2 come from a table that forms a recordset. The query result shown in the figure is the data for all authors.

Figure 2:biblio The authors table for the database, and the selected row is related to authors records

Note: Records can be viewed as a tool for browsing databases, where users can specify the data they want to select, and there are three types of recordsets:
(1) Dynasets: This is a modifiable display of data;
(2) Snapshots: This is static (read-only) display data;
(3) Tables: This is the direct display data for the table.
Dynasets and snapshots are typically generated in SQL (Structured Query Language) statements, which are described later, but now just know that SQL statements are standard commands for reading data from a specified database. Dynasets is updated each time the user database, and changes to the recordset are reflected in the underlying table. Snapshots is a static display of the same data that contains the records requested when the snapshots is generated (changes in the underlying table are not reflected in the snapshots) and will naturally not change snapshots.
Dynasets is the most flexible and powerful set of records. Although the table type Recordset requires significant overhead costs. Snapshots is the most inflexible set of records, but has the least overhead cost. If you do not need to update the database, you can use snapshots this type as long as you browse the record.
The snapshots type also has a deformable forward type snapshots, which is snapshots more restrictive and can only move forward, but faster. Forward type snapshots can be used to scan multiple records and sequentially process (perform numeric calculations, copy the selected records to another table, and so on) to record the database. This recordset does not provide a reverse approach, so indirect costs are low.
Table-type record groups can be used to invoke database tables. Tables work faster than other recordset types, keeping tables synchronized with data in the database, and can be used to update databases. But the table is limited to one table. In addition, when you access a table through a tables recordset, you can use the index value of tables to make a quick lookup.

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