SQL Fundamentals

The OR operator returns TRUE when at least one of the conditions is TRUE. This includes cases where either one condition is TRUE, or both conditions are TRUE simultaneously. Option D correctly states this behavior by combining both scenarios.

ROLLBACK is the SQL command that undoes all changes made during the current transaction, restoring the database to its state before the transaction began. COMMIT permanently saves changes, while DROP deletes database objects and SAVEPOINT marks intermediate points within a transaction.

Constraints in SQL are rules enforced on table columns to ensure data integrity and prevent invalid data entry. Common constraints include PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, and CHECK. They are not used for writing programs or creating data types.

A composite key is a primary key that consists of two or more columns used together to uniquely identify each record in a table. A foreign key references another table's primary key, an alternate key is a candidate key not chosen as primary key, and 'duplicate key' is not a standard database term.

A VIEW is a virtual table based on the result-set of a SELECT query. It contains no stored data itself - data is generated dynamically when the view is queried. Option C correctly captures both characteristics: views don't store data (option A) and are mapped to SELECT statements (option B).

The UNIQUE constraint ensures that all values in a column are different - no two rows can have the same value for that column. DISTINCT is used in SELECT queries to remove duplicates from results, CHECK validates values against a condition, and these are not the correct constraint for preventing repeated values.

A PRIMARY KEY must contain unique values and cannot contain NULL values. Option D 'none of these' is correct because options A, B, and C all describe what a primary key must NOT do - it cannot contain NULL values, cannot contain repetitive values, and certainly cannot contain both.

ADO (ActiveX Data Objects) defines standard data types like adBigInt, adCurrency, and adWChar. However, adUID is not a valid ADO data type in the enumeration - this appears to be a fabricated option to test knowledge of the actual ADO type system.

SELECT INTO is a SQL command (particularly in SQL Server) that creates a new table and populates it with the result set from a query, effectively creating a backup. CREATE INTO and CREATE FROM are not valid SQL syntax for this purpose.

The SELECT...INTO statement is the correct SQL syntax to create a new table in another database from existing data. Options A and C use invalid CREATE TABLE syntax (no FROM clause in this context).

The IN operator in SQL tests whether a value matches any value in a specified list or any value returned by a subquery. It is not limited to DISTINCT or INSERT keywords, and FROM (not IN) defines the tables for SELECT or DELETE operations.

ADO stands for ActiveX Data Objects, which is Microsoft's data access technology for connecting applications to various data sources. It is not Active Database Objects, Active Directory Object (that's a Windows Server technology), or Advanced Data Object.

The UPDATE statement modifies all rows that satisfy the WHERE clause. If the WHERE condition matches multiple rows (or is omitted entirely), the UPDATE affects all matching rows simultaneously, not just one.

The bcp (bulk copy program) utility in SQL Server bypasses triggers by default for performance. During bulk import operations, triggers are not fired unless specifically configured otherwise.

SQL is an industry-standard language designed for managing and manipulating relational databases. The name literally describes its purpose: a structured language for querying data.

DDL (Data Definition Language) defines database structures. CREATE builds objects like tables, views, and indexes. INSERT and UPDATE are DML (data manipulation), while COMMIT is TCL (transaction control).

Indexes create data structures that allow the database engine to find specific rows quickly without scanning entire tables. They optimize record retrieval based on column values.

In SQL databases, a column with no value stores NULL, which represents missing or unknown data. NULL is different from zero, a blank string, or an empty value - it is the absence of a value.

INSERT is the standard SQL command for adding new records (rows) to a table. It specifies which table to modify and provides values for the columns.

UPDATE modifies existing data in a database. It changes values in specified columns for rows that match the WHERE condition, allowing targeted changes to existing records.

DROP completely removes a table and its structure from the database, including all data, indexes, and constraints. DELETE removes only the data rows while preserving the table structure.

SELECT is the primary SQL command for retrieving and querying data from databases. It specifies which columns to fetch and from which tables, with optional filtering and sorting.

DDL stands for Data Definition Language, the subset of SQL commands that define database structures (CREATE, DROP, ALTER). DML manipulates data, DCL controls permissions, and TCL manages transactions.

COMMIT is a TCL (Transaction Control Language) command, not DDL, DML, or DCL. It permanently saves changes made during a transaction. Since TCL is not listed, 'None of these' is technically correct.

The AND operator in programming and logic returns TRUE only when ALL conditions being evaluated are true. If even one condition is false, the entire AND expression becomes false. Option A correctly states this fundamental behavior.