Character Data Types: • CHAR Data Type • VARCHAR2 Data Type • VARCHAR Data Type • NUMBER Data Type CHAR Data Type The CHAR data type specifies a fixed-length character string in the database character set. You specify the database character set when you create your database. When you create a table with a CHAR … Read more
Primary Key Constraints A primary key constraint designates a column as the primary key of a table or view. A composite primary key designates a combination of columns as the primary key. A primary key can be natural or a surrogate. A natural key is a meaningful identifier made of existing attributes in a table. … Read more
Data Concurrency A requirement of a multiuser RDBMS is the control of data concurrency, which is the simultaneous access of the same data by multiple users. Without concurrency controls, users could change data improperly, compromising data integrity. For example, one user could update a row while a different user simultaneously updates it. If multiple users … Read more
A transaction is a logical, atomic unit of work that contains one or more SQL statements. A transaction groups SQL statements so that they are either all committed, which means they are applied to the database, or all rolled back, which means they are undone from the database. Oracle Database assigns every transaction a unique … Read more
Data Consistency In Oracle Database, each user must see a consistent view of the data, including visible changes made by a user’s own transactions and committed transactions of other users. For example, the database must prevent the dirty read problem, which occurs when one transaction sees uncommitted changes made by another concurrent transaction. Oracle Database … Read more
Structured Query Language (SQL) is the set of statements with which all programs and usersaccess data in an Oracle Database. Application programs and Oracle tools often allow usersaccess to the database without using SQL directly, but these applications in turn must useSQL when executing the user’s request. SQL is a set-based declarative language that provides … Read more
In Oracle Database, a database schema is a collection of logical data structures, or schema objects. A database user owns a database schema, which has the same name as the user name. Schema objects are user-created structures that directly refer to the data in the database. The database supports many types of schema objects, the … Read more
The pattern-matching conditions compare character data. LIKE Condition * The LIKE conditions specify a test involving pattern matching. Whereas the equality operator (=) exactly matches one character value to another. * The LIKE conditions match a portion of one character value to another by searching the first value for the pattern specified by the second. … Read more
The dynamic performance views are special views that are continuously updated while a database is open and in use. Throughout its operation, Oracle Database maintains a set of virtual tables that record current database activity.These views are dynamic because they are continuously updated while a database is open and in use. The views are sometimes … Read more
A check constraint on a column or set of columns requires that a specified condition be true or unknown for every row. A check constraint lets you specify a condition that each row in the table must satisfy. To satisfy the constraint, each row in the table must make the condition either TRUE or unknown … Read more