SQL------ Commands And Functions

Comparison Operators

For numbers (INT, DECIMAL, FLOAT), you could use comparison operators: '=' (equal to),
'<>' or '!=' (not equal to), '>' (greater than), '<' (less than), '>=' (greater than or equal to),
'<=' (less than or equal to), to compare two numbers. For example, price > 1.0, quantity
<= 500.
mysql> SELECT name, price FROM products WHERE price < 1.0;
+-----------+-------+
| name | price |
+-----------+-------+
| Pencil 2B | 0.48 |
| Pencil 2H | 0.49 |
+-----------+-------+
2 rows in set (0.00 sec)
mysql> SELECT name, quantity FROM products WHERE quantity <= 2000;
+-----------+----------+
| name | quantity |
+-----------+----------+
| Pen Black | 2000 |
+-----------+----------+
1 row in set (0.00 sec)

String Pattern Matching - LIKE and NOT LIKE

For strings, in addition to full matching using operators like '=' and '<>', we can perform
pattern matching using operator LIKE (or NOT LIKE) with wildcard characters. The wildcard
'_' matches any single character; '%' matches any number of characters (including zero). For
example,
• 'abc%' matches strings beginning with 'abc';
• '%xyz' matches strings ending with 'xyz';
• '%aaa%' matches strings containing 'aaa';
• '___' matches strings containing exactly three characters; and
• 'a_b%' matches strings beginning with 'a', followed by any single character, followed by
'b', followed by zero or more characters.



-- "name" begins with 'PENCIL'
mysql> SELECT name, price FROM products WHERE name LIKE 'PENCIL%';
+-----------+-------+
| name | price |
+-----------+-------+
| Pencil 2B | 0.48 |
| Pencil 2H | 0.49 |
+-----------+-------+
-- "name" begins with 'P', followed by any two characters,
-- followed by space, followed by zero or more characters
mysql> SELECT name, price FROM products WHERE name LIKE 'P__ %';
+-----------+-------+
| name | price |
+-----------+-------+
| Pen Red | 1.23 |
| Pen Blue | 1.25 |
| Pen Black | 1.25|
MySQL also support regular expression matching via the REGEXE operator.

Logical Operators - AND, OR, NOT, XOR

You can combine multiple conditions with boolean operators AND, OR, XOR. You can also invert a
condition using operator NOT. For examples,
mysql> SELECT * FROM products WHERE quantity >= 5000 AND name LIKE 'Pen %';
+-----------+-------------+----------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+----------+----------+-------+
| 1001 | PEN | Pen Red | 5000 | 1.23 |
| 1002 | PEN | Pen Blue | 8000 | 1.25 |
+-----------+-------------+----------+----------+-------+
mysql> SELECT * FROM products WHERE quantity >= 5000 AND price < 1.24 AND name
LIKE 'Pen %';
+-----------+-------------+---------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+---------+----------+-------+
| 1001 | PEN | Pen Red | 5000 | 1.23 |
+-----------+-------------+---------+----------+-------+
mysql> SELECT * FROM products WHERE NOT (quantity >= 5000 AND name LIKE 'Pen
%');
+-----------+-------------+-----------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+-----------+----------+-------+
| 1003 | PEN | Pen Black | 2000 | 1.25 |
| 1004 | PEC | Pencil 2B | 10000 | 0.48 |
| 1005 | PEC | Pencil 2H | 8000 | 0.49 |
+-----------+-------------+-----------+----------+-------+
IN, NOT IN
You can select from members of a set with IN (or NOT IN) operator. This is easier and clearer than
the equivalent AND-OR expression.
mysql> SELECT * FROM products WHERE name IN ('Pen Red', 'Pen Black');
+-----------+-------------+-----------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+-----------+----------+-------+
| 1001 | PEN | Pen Red | 5000 | 1.23 |
| 1003 | PEN | Pen Black | 2000 | 1.25 |
+-----------+-------------+-----------+----------+-------+

BETWEEN, NOT BETWEEN

To check if the value is within a range, you could use BETWEEN ... AND ... operator. Again,
this is easier and clearer than the equivalent AND-OR expression.
mysql> SELECT * FROM products
WHERE (price BETWEEN 1.0 AND 2.0) AND (quantity BETWEEN 1000 AND 2000);
+-----------+-------------+-----------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+-----------+----------+-------+
| 1003 | PEN | Pen Black | 2000 | 1.25 |
+-----------+-------------+-----------+----------+-------+


ORDER BY Clause

You can order the rows selected using ORDER BY clause, with the following syntax:
SELECT ... FROM tableName
WHERE criteria
ORDER BY columnA ASC|DESC, columnB ASC|DESC, ...
The selected row will be ordered according to the values in columnA, in either ascending (ASC)
(default) or descending (DESC) order. If several rows have the same value in columnA, it will be
ordered according to columnB, and so on. For strings, the ordering could be case-sensitive or caseinsensitive,
depending on the so-called character collating sequence used. For examples,
-- Order the results by price in descending order
mysql> SELECT * FROM products WHERE name LIKE 'Pen %' ORDER BY price DESC;
+-----------+-------------+-----------+----------+-------+
| productID | productCode | name | quantity | price |
+-----------+-------------+-----------+----------+-------+
| 1002 | PEN | Pen Blue | 8000 | 1.25 |
| 1003 | PEN | Pen Black | 2000 | 1.25 |
| 1001 | PEN | Pen Red | 5000 | 1.23 |
+-----------+-------------+-----------+----------+-------+