Oracle Learning - 2

SQL: Combining the "AND" and "OR" Conditions

The AND and OR conditions can be combined in a single SQL statement. It can be used in any valid SQL statement - select, insert, update, or delete.
When combining these conditions, it is important to use brackets so that the database knows what order to evaluate each condition.


Example #1
The first example that we'll take a look at an example that combines the AND and OR conditions.
SELECT *
FROM supplier
WHERE (city = 'New York' and name = 'IBM')
or (city = 'Newark');
This would return all suppliers that reside in either New York whose name is IBM, all supplies that reside in Newark. The brackets determine what order the AND and OR conditions are evaluated in.

Example #2
The next example takes a look at a more complex statement.
For example:
SELECT supplier_id
FROM supplier
WHERE (name = 'IBM')
or (name = 'Hewlett Packard' and city = 'Atlantic City')
or (name = 'Gateway' and status = 'Active' and city = 'Burma');
This SQL statement would return all supplier_id values where the supplier's name is IBM or the name is Hewlett Packard and the city is Atlantic City or the name is Gateway and the city is Burma.
SQL: LIKE Condition

The LIKE condition allows you to use wildcards in the where clause of an SQL statement. This allows you to perform pattern matching. The LIKE condition can be used in any valid SQL statement - select, insert, update, or delete.
The patterns that you can choose from are:
% allows you to match any string of any length (including zero length)
_ allows you to match on a single character

Examples using % wildcard
The first example that we'll take a look at involves using % in the where clause of a select statement. We are going to try to find all of the suppliers whose name begins with 'Hew'.
SELECT * FROM supplier
WHERE supplier_name like 'Hew%';


You can also using the wildcard multiple times within the same string. For example,
SELECT * FROM supplier
WHERE supplier_name like '%bob%';
In this example, we are looking for all suppliers whose name contains the characters 'bob'.

You could also use the LIKE condition to find suppliers whose name does not start with 'T'. For example,
SELECT * FROM supplier
WHERE supplier_name not like 'T%';
By placing the not keyword in front of the LIKE condition, you are able to retrieve all suppliers whose name does not start with 'T'.

Examples using _ wildcard
Next, let's explain how the _ wildcard works. Remember that the _ is looking for only one character.
For example,
SELECT * FROM supplier
WHERE supplier_name like 'Sm_th';
This SQL statement would return all suppliers whose name is 5 characters long, where the first two characters is 'Sm' and the last two characters is 'th'. For example, it could return suppliers whose name is 'Smith', 'Smyth', 'Smath', 'Smeth', etc.

Here is another example,
SELECT * FROM supplier
WHERE account_number like '12317_';
You might find that you are looking for an account number, but you only have 5 of the 6 digits. The example above, would retrieve potentially 10 records back (where the missing value could equal anything from 0 to 9). For example, it could return suppliers whose account numbers are:
123170
123171
123172
123173
123174
123175
123176
123177
123178
123179.


Examples using Escape Characters
Next, in Oracle, let's say you wanted to search for a % or a _ character in a LIKE condition. You can do this using an Escape character.
Please note that you can define an escape character as a single character (length of 1) ONLY.
For example,
SELECT * FROM supplier
WHERE supplier_name LIKE '!%' escape '!';
This SQL statement identifies the ! character as an escape character. This statement will return all suppliers whose name is %.

Here is another more complicated example:
SELECT * FROM supplier
WHERE supplier_name LIKE 'H%!%' escape '!';
This example returns all suppliers whose name starts with H and ends in %. For example, it would return a value such as 'Hello%'.

You can also use the Escape character with the _ character. For example,
SELECT * FROM supplier
WHERE supplier_name LIKE 'H%!_' escape '!';
This example returns all suppliers whose name starts with H and ends in _. For example, it would return a value such as 'Hello_'.
SQL: "IN" Function

The IN function helps reduce the need to use multiple OR conditions.
The syntax for the IN function is:
SELECT columns
FROM tables
WHERE column1 in (value1, value2, .... value_n);
This SQL statement will return the records where column1 is value1, value2..., or value_n. The IN function can be used in any valid SQL statement - select, insert, update, or delete.


Example #1
The following is an SQL statement that uses the IN function:
SELECT *
FROM supplier
WHERE supplier_name in ( 'IBM', 'Hewlett Packard', 'Microsoft');
This would return all rows where the supplier_name is either IBM, Hewlett Packard, or Microsoft. Because the * is used in the select, all fields from the supplier table would appear in the result set.
It is equivalent to the following statement:
SELECT *
FROM supplier
WHERE supplier_name = 'IBM'
OR supplier_name = 'Hewlett Packard'
OR supplier_name = 'Microsoft';
As you can see, using the IN function makes the statement easier to read and more efficient.

Example #2
You can also use the IN function with numeric values.
SELECT *
FROM orders
WHERE order_id in (10000, 10001, 10003, 10005);
This SQL statement would return all orders where the order_id is either 10000, 10001, 10003, or 10005.
It is equivalent to the following statement:
SELECT *
FROM orders
WHERE order_id = 10000
OR order_id = 10001
OR order_id = 10003
OR order_id = 10005;

Example #3 - "NOT IN"
The IN function can also be combined with the NOT operator.
For example,
SELECT *
FROM supplier
WHERE supplier_name not in ( 'IBM', 'Hewlett Packard', 'Microsoft');
This would return all rows where the supplier_name is neither IBM, Hewlett Packard, or Microsoft. Sometimes, it is more efficient to list the values that you do not want, as opposed to the values that you do want.