SQL COMMANDS LATEST STUDY GUIDE

SQL COMMANDS LATEST STUDY GUIDE
The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set. ans: SELECT column_name,column_name
FROM table_name;

SELECT * FROM table_name;

The SELECT DISTINCT statement is used to return only distinct (different) values ans: SELECT DISTINCT
column_name,column_name
FROM table_name;

The WHERE clause is used to extract only those records that fulfill a specified criterion. ans: SELECT
column_name,column_name
FROM table_name
WHERE column_name operator value;

he AND operator displays a record if both the first condition AND the second condition are true.

The OR operator displays a record if either the first condition OR the second condition is true. ans:
SELECT * FROM Customers
WHERE Country='Germany'
AND City='Berlin';

The ORDER BY keyword is used to sort the result-set. ans: SELECT column_name, column_name
FROM table_name
ORDER BY column_name ASC|DESC, column_name ASC|DESC;

The INSERT INTO statement is used to insert new records in a table. ans: INSERT INTO table_name
(column1,column2,column3,...)
VALUES (value1,value2,value3,...);

The UPDATE statement is used to update records in a table. ans: UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;

The DELETE statement is used to delete records in a table. ans: DELETE FROM table_name
WHERE some_column=some_value;

SQL injection is a technique where malicious users can inject SQL commands into an SQL statement, via
web page input.

Injected SQL commands can alter SQL statement and compromise the security of a web application. ans:
txtUserId = getRequestString("UserId");
txtSQL = "SELECT * FROM Users WHERE UserId = " + txtUserId;

, The SELECT TOP clause is used to specify the number of records to return.

The SELECT TOP clause can be very useful on large tables with thousands of records. Returning a large
number of records can impact on performance. ans: SELECT TOP number|percent column_name(s)
FROM table_name;

The LIKE operator is used in a WHERE clause to search for a specified pattern in a column. ans: SELECT
column_name(s)
FROM table_name
WHERE column_name LIKE pattern;

% A substitute for zero or more characters
_ A substitute for a single character
[charlist] Sets and ranges of characters to match
[^charlist]
or
[!charlist] Matches only a character NOT specified within the brackets ans: SQL wildcards

The IN operator allows you to specify multiple values in a WHERE clause. ans: SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1,value2,...);

The BETWEEN operator selects values within a range. The values can be numbers, text, or dates. ans:
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

SQL aliases are used to give a database table, or a column in a table, a temporary name.

Basically aliases are created to make column names more readable ans: SELECT column_name AS
alias_name
FROM table_name;

The INNER JOIN keyword selects all rows from both tables as long as there is a match between the
columns in both tables. ans: SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name=table2.column_name;

The LEFT JOIN keyword returns all rows from the left table (table1), with the matching rows in the right
table (table2). The result is NULL in the right side when there is no match. ans: SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name=table2.column_name;

The RIGHT JOIN keyword returns all rows from the right table (table2), with the matching rows in the left
table (table1). The result is NULL in the left side when there is no match. ans: SELECT column_name(s)
FROM table1