SQL Database Queries and Operations

The SELECT statement is the fundamental SQL command used to retrieve or extract data from database tables. Options B, C, and D (GET, OPEN, EXTRACT) are not valid SQL statements for querying data. This is basic SQL syntax that every database user must know.

The UPDATE statement is the SQL command used to modify existing data in database tables. Options A, B, and D (SAVE, MODIFY, SAVE AS) are not valid SQL statements - these sound like application commands, not database operations. UPDATE is paired with SET and WHERE clauses to change specific records.

The INSERT statement is the SQL command used to add new records to database tables. Options A, B, and D (ADD RECORD, ADD NEW, INSERT NEW) are not valid SQL syntax. The correct command is simply INSERT, typically used with INSERT INTO followed by VALUES or a SELECT statement.

The correct SQL syntax to select all columns is 'SELECT * FROM tablename' where the asterisk (*) is a wildcard representing all columns. Option A incorrectly uses square brackets, option B has an erroneous period after the asterisk, and option C has incorrect dot notation. The semicolon at the end is optional but correct.

The correct syntax is 'SELECT * FROM Persons WHERE FirstName='Peter'' which uses the WHERE clause with an equality operator. Option A incorrectly uses square brackets, while options C and D use LIKE operator which is for pattern matching, not exact values. The WHERE clause filters rows based on specified conditions.

The correct syntax is 'SELECT * FROM Persons WHERE FirstName LIKE 'a%'' which uses the LIKE operator with a wildcard pattern. The percent sign (%) matches any sequence of characters, so 'a%' finds strings starting with 'a'. Option A finds strings ending with 'a', option B checks for exact equality, and option D has incorrect syntax with misplaced quotes and wildcard.

The ORDER BY clause is the correct SQL keyword combination for sorting query results. 'ORDER' or 'SORT BY' alone are not valid SQL syntax for sorting.

In SQL, sorting is performed using the ORDER BY clause, and descending order is specified with the DESC keyword. Therefore, ORDER BY FirstName DESC is correct. The other options use non-existent or invalid SQL keywords like SORT or omit the required BY keyword.

UPDATE table SET column=value WHERE condition is the standard SQL syntax. MODIFY and INTO are not valid keywords in UPDATE statements.

To solve this question, the user needs to know the basic syntax for deleting records in SQL, including the correct use of the DELETE command and WHERE clause.

Now, let's go through each option and explain why it is right or wrong:

A. DELETE FROM Persons WHERE FirstName = 'Peter' ;
This option is correct. The DELETE command is used to delete records from a table in SQL. The WHERE clause is used to specify the condition that must be met for a record to be deleted. In this case, we want to delete all records where the FirstName is Peter, so we use the WHERE FirstName = 'Peter' condition.

B. DELETE FirstName='Peter' FROM Persons;
This option is incorrect. The correct syntax for the DELETE command is DELETE FROM table_name, followed by the WHERE clause. In this option, the syntax is incorrect because the table name is missing, and the condition is in the wrong place.

C. DELETE ROW FirstName='Peter' FROM Persons ;
This option is incorrect. The correct syntax for the DELETE command is DELETE FROM table_name, followed by the WHERE clause. In this option, the syntax is incorrect because the ROW keyword is not used in the correct way.

D. TRUNCATE FROM Persons WHERE FirstName='Peter'
This option is incorrect. The TRUNCATE command is used to delete all records from a table, not specific records that meet a certain condition. Also, the syntax is incorrect because the WHERE clause is used in the wrong place.

The Answer is: A. DELETE FROM Persons WHERE FirstName = 'Peter' ;

COUNT(*) is the SQL aggregate function that returns the total number of rows. COLUMNS is not a valid SQL keyword, and COUNT() requires parentheses with an argument.