SQL and Database Fundamentals

SQL stands for Structured Query Language, the standard language for managing and manipulating relational databases. It's used for querying, updating, and managing data in database systems. Options B and C incorrectly use 'Question' instead of 'Query'.

The SELECT statement is the fundamental SQL command used to retrieve and extract data from database tables. It allows you to specify which columns and rows you want to retrieve. Options A, B, and D are not valid SQL statements for data retrieval.

The DELETE statement is used to remove rows from a database table. You can delete specific rows using a WHERE clause or all rows if no condition is specified. Options B (COLLAPSE) and C (REMOVE) are not valid SQL statements.

The SELECT statement is used to extract or retrieve data from a database. It's the primary query command in SQL that allows you to specify columns and conditions for data retrieval. Options A (OPEN), B (GET), and D (EXTRACT) are not correct SQL statements for querying data.

The UPDATE statement is used to modify existing data in a database table. It allows you to change values in specific columns for rows that match a given condition. Options A (SAVE), B (SAVE AS), and C (MODIFY) are not valid SQL statements for updating data.

The standard SQL statement used to add new records to a database table is 'INSERT INTO'. 'INSERT NEW', 'ADD RECORD', and 'ADD NEW' are syntactically invalid in standard SQL.

To select all columns from a table, you use SELECT * followed by FROM and the table name. The asterisk () is a wildcard that represents all columns in the table. Option A only selects the table name (not columns), B has incorrect syntax (.Persons), and D uses non-existent [all] syntax.

To select records where a column equals a specific value, use SELECT * FROM table WHERE column='value'. The correct syntax uses single quotes for string values and the equals operator. Option A uses <> (not equals), B uses invalid [all] syntax, and D uses LIKE which is for pattern matching, not exact matches.

SQL stands for Structured Query Language, the standard language for relational database management systems. It's used for querying, updating, and managing data. Options B and C incorrectly substitute 'Question' for 'Query'.

To select a specific column from a table, use SELECT column_name FROM table_name. This retrieves only the specified column for all rows. Option A uses incorrect dot notation (Persons.FirstName), C uses non-existent EXTRACT keyword, and the syntax for column selection is simply SELECT followed by the column name.

Primary Key constraints cannot contain NULL values by definition. Each row must have a unique, non-NULL identifier. This is a fundamental property of primary keys in relational databases.

Secondary keys are used for indexing and identification in databases. By definition, any key (primary or secondary) cannot contain NULL values because keys must uniquely identify or index records - a NULL value would defeat this purpose.

A composite key combines multiple columns to create a unique identifier. The entire combination cannot be NULL, though individual components might allow NULLs in some systems. For the key to function as an identifier, at least one component must be non-NULL.

DB2 is IBM's family of database management systems. It's a commercial RDBMS that supports SQL, manages structured data, and is widely used in enterprise environments for transaction processing and data warehousing.

ORDER BY is the SQL clause used to sort query results in ascending (ASC) or descending (DESC) order based on one or more columns. Options like SORT BY or just ORDER/SORT are not valid SQL syntax.

The UPDATE statement modifies existing data in a table. The correct syntax is UPDATE table_name SET column=new_value WHERE condition. Option D correctly changes 'Hansen' to 'Nilsen' for all matching rows. MODIFY is not a valid SQL keyword.

COUNT() is an aggregate function that returns the total number of rows in a table. The asterisk () indicates count all rows regardless of NULL values. Options B, C, and D use incorrect syntax (COLUMNS is not a valid SQL keyword, and COUNT() requires the * parameter).

SELECT * retrieves all columns, and WHERE FirstName='Peter' filters for exact matches. The = operator is for exact matching (not LIKE, which is for patterns). Options A and C incorrectly use [all] instead of *, and option B uses <> (not equal) which would exclude 'Peter'.

The LIKE operator with 'a%' matches any string starting with 'a' followed by any characters. The % is a wildcard representing zero or more characters. Option A's '%a' matches ending with 'a', B's syntax is invalid, C matches only exact 'a', and D's 'a%' correctly matches starting with 'a'.