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SQL Database:
So, an SQL database is one whose symbols are organized into a collection of tables. Now, shows an SQL table as the current value of an SQL variable, ENROLMENT, but in that connection there are two important points to be made right away. First, the term table variable isn't used in SQL for its counterpart of relation variables. Instead, base relvars are normally referred to as base tables, virtual relvars as views (or viewed tables) and those terms are used in the international standard. Secondly, not every SQL table can be the value of a base table or view. As we shall soon see, table variables and the tables assigned to them are subject to several deviations from relational theory; tables that cannot be assigned to a variable are subject to even more deviations.
Keys in SQL SQL support for keys in the following respects: SQL does not require at least one key for every base table. If no key is explicitly declared, then KEY {ALL B
Using Pragma RESTRICT_REFERENCES: The function called from the SQL statements should obey certain rules meant to control the side effects. To check for violation of the rules,
Initializing and Referencing Collections Until you initialize a collection, a nested table or varray is automatically null (i.e. the collection itself is null, not its elements)
Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system
Transaction context As the figure shows, the major transaction shares its context with the nested transactions, but not with the autonomous transactions. Similarly, If one aut
GOTO Statement The GOTO statement branches to a label unconditionally. The label must be exclusive within its scope and should precede an executable statement or a PL/SQL block.
CHECK Constraints in SQL A CHECK constraint is a table constraint defined using the key word CHECK, as already illustrated in several examples in this chapter. In particular,
SQL Is a Database Language: The commands given to a DBMS by an application are written in the database language of the DBMS. The term data sublanguage is sometimes used instea
Effects of NULL for UNIQUE Specification When a UNIQUE specification u for base table t includes a column c that is not subject to a NOT NULL constraint, the appearance of sev
Cursor Variables Similar to a cursor, cursor variable points to the current row in the result set of a multi-row query. But, dissimilar a cursor, a cursor variable can be opene
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