Question

1. In SELECT statements, what are the comparison operands? Provide a SELECT example 2. In a SELECT statement, what is a wildcard? Provide a SELECT example 3. In a SELECT statement how would you escape a wildcard? Provide a SELECT example 4. What does the NATURAL LANGUAGE mode in a where clause do? 5. What is an aggregate function in the SELECT? Provide a SELECT example 6. Could I create a new column in a SELECT clause? If yes, provide a SELECT example 7. How would I rename a column in the SELECT statement? 8. What is the difference between ALTER table and UPDATE? 9. How would I get the unique values in a column of a table? Provide a SELECT example 10. What are 2 ways I could insert rows to a table, using the SELECT statement.

Answer 1

1.

A comparison (or relational) operator is a mathematical symbol which is used to compare two values.

Comparison operators are used in conditions that compares one expression with another. The result of a comparison can be TRUE, FALSE, or UNKNOWN (an operator that has one or two NULL expressions returns UNKNOWN).

Example:

To get a comparison between two numbers from the DUAL table, the following SQL statement can be used :

SELECT 15>14 FROM dual;

2.

A wildcard character is used to substitute any other character(s) in a string.

Wildcard characters are used with the SQL LIKE operator. The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.

There are two wildcards used in conjunction with the LIKE operator:

• % - The percent sign represents zero, one, or multiple characters
• _ - The underscore represents a single character

Example:

The following SQL statement selects all customers with a City starting with "ber":

SELECT * FROM Customers
WHERE City LIKE 'ber%';

3. The purpose of the escape clause is to stop the wildcard characters (eg. % or _) from being considered as wildcards.

Example:

We can find all the records with a percentage sign in a part number by escaping the middle of three percentage signs with an equal sign:

SELECT * FROM partno WHERE part LIKE '%=%%' ESCAPE '=';

4. By default or with the IN NATURAL LANGUAGE MODE modifier, the MATCH() function performs a natural language search for a string against a text collection. A collection is a set of one or more columns included in a FULLTEXT index. The search string is given as the argument to AGAINST(). For each row in the table, MATCH() returns a relevance value; that is, a similarity measure between the search string and the text in that row in the columns named in the MATCH() list.

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