In SQL, three commands can be used to modify the database: INSERT, DELETE, and UPDATE. We discuss each of these in turn. The INSERT Command In its simplest form, INSERT is used to add a single tuple to a relation. We must specify the relation name and a list of values for the tuple. The
Insert, Delete, and Update Statements in SQL Read More »
Consider a reciprocating engine mechanism OCP shown in Fig, the piston mass at P of the reciprocating parts is accelerating. Thus a primary force is required to accelerate the reciprocating mass. This force acts in a direction from P to O. The reaction of this force tends to move the frame in a direction from
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A reciprocating engine say, an IC engine has both rotating and reciprocating parts. The rotating masses in a single cylinder and a multi cylinder can be balanced using the methods already discussed in the previous chapter. The unbalanced reciprocating masses will produce a shaking force (unbalanced force) and a shaking couple (couple due to the
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In the following sections, the frequency of transverse vibrations of various systems and the phenomenon of whirling speed have been discussed. Natural Frequency of Free Transverse Vibrations Consider a shaft of negligible mass, whose one end is fixed and the other end carries a body of weight W, as shown in Fig (a). Fig (b)
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SQL uses the terms table, row, and column for the formal relational model terms relation, tuple, and attribute, respectively. We will use the corresponding terms interchangeably. The main SQL command for data definition is the CREATE statement, which can be used to create schemas, tables (relations), and domains (as well as other constructs such as
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So far, we have discussed the characteristics of single relations. In a relational database, there will typically be many relations, and the tuples in those relations are usually related in various ways. The state of the whole database will correspond to the states of all its relations at a particular point in time. There are
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The relational model represents the database as a collection of relations. Informally, each relation resembles a table of values or, to some extent, a flat file of records. It is called a flat file because each record has a simple linear or flat structure. For example, the database of files that was shown in Figure
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Several criteria are normally used to classify DBMSs. The first is the data model on which the DBMS is based. The main data model used in many current commercial DBMSs is the relational data model. The object data model has been implemented in some commercial systems but has not had widespread use. Many legacy applications
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Centralized DBMSs Architecture Architectures for DBMSs have followed trends similar to those for general computer system architectures. Earlier architectures used mainframe computers to provide the main processing for all system functions, including user application programs and user interface programs, as well as all the DBMS functionality. The reason was that most users accessed such systems
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A DBMS is a complex software system. In this section we discuss the types of software components that constitute a DBMS and the types of computer database system software with which the DBMS interacts. DBMS Component Modules Figure illustrates, in a simplified form, the typical DBMS components. The figure is divided into two parts. The
The Database System Environment Read More »