Showing posts with label MySQL. Show all posts
Showing posts with label MySQL. Show all posts

Data Manipulation Language (DML) statements ?

01:53
  • Data Manipulation Language (DML) statements  Allow you to modify the contents of tables. There are three DML statements:
    • INSERT  Allows you to add rows to a table.
    • UPDATE  Allows you to change a row.
    • DELETE  Allows you to remove rows.
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What Is a Relational Database?

01:52
The basic concepts of a relational database are fairly easy to understand. A relational database is a collection of related information that has been organized into structures known as tables. Each table contains rows that are further organized into columns. These tables are stored in the database in structures known as schemas, which are areas where database users may store their tables. Each user may also choose to grant permissions to other users to access their tables.
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MySQL Subqueries?

05:07

You can use the result of a query like you use a list of values with the IN operator to filter a query based on the result of another query. The subquery appears in parentheses after the IN keyword.
The following query fetches all columns from the products table, but only for those product codes that were part of order number 1:

mysql> SELECT *
    -> FROM products
    -> WHERE product_code IN (
    ->   SELECT product_code
    ->   FROM order_lines
    ->   WHERE order_id = 1
    -> );
+--------------+---------------+--------+--------+
| product_code | name          | weight | price  |
+--------------+---------------+--------+--------+
| MINI         | Small product |   1.50 |  5.99  |
| MAXI         | Large product |   8.00 | 15.99  |
+--------------+---------------+--------+--------+
2 rows in set (0.00 sec)
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MySQL Triggers

05:05
To create a new trigger, use the CREATE TRIGGER statement. You must give the trigger a unique name and then provide the timing, action, and table that will cause the trigger to fire. For example, to create a trigger that will fire every time a row is deleted from the products table, you would construct a trigger as follows:
 
CREATE TRIGGER trigger_name
BEFORE DELETE ON products
FOR EACH ROW
BEGIN
  ...
END



The timing for a trigger can be BEFORE or AFTER, indicating whether the trigger code should be executed immediately before or immediately after the SQL statement that causes the trigger to fire.
The keywords FOR EACH ROW are part of the CREATE TRIGGER syntax and are required in every trigger.
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what is Triggers?

05:04
A trigger is a stored database object that contains a series of SQL commands, set to activate automatically when certain events take place.
Each trigger is associated with a table. You can create a trigger that will fire when an INSERT, UPDATE, or DELETE takes place on the named table.
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What Is SQL?

05:02
The Structured Query Language (SQL) is the most common way to retrieve and manage database information. An SQL query consists of a series of keywords that define the data set you want to fetch from the database. SQL uses descriptive English keywords, so most queries are easy to understand.
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Learning the MySQL Data Types

03:59
MySQL uses many different data types, broken into three categories: numeric, date and time, and string types.

 INT—A normal-sized integer that can be signed or unsigned. If signed, the
allowable range is from –2147483648 to 2147483647. If unsigned, the allowable
range is from 0 to 4294967295. You can specify a width of up to 11 digits.

. TINYINT—A small integer that can be signed or unsigned. If signed, the allowable
range is from –128 to 127. If unsigned, the allowable range is from 0 to
255. You can specify a width of up to 4 digits.

 SMALLINT—A small integer that can be signed or unsigned. If signed, the
allowable range is from –32768 to 32767. If unsigned, the allowable range is
from 0 to 65535. You can specify a width of up to 5 digits.

 MEDIUMINT—A medium-sized integer that can be signed or unsigned. If signed,
the allowable range is from –8388608 to 8388607. If unsigned, the allowable
range is from 0 to 16777215. You can specify a width of up to 9 digits.

 BIGINT—A large integer that can be signed or unsigned. If signed, the allowable
range is from –9223372036854775808 to 9223372036854775807. If
unsigned, the allowable range is from 0 to 18446744073709551615. You can
specify a width of up to 11 digits.

FLOAT(M,D)—A floating-point number that cannot be unsigned. You can
define the display length (M) and the number of decimals (D). This is not
required and defaults to 10,2, where 2 is the number of decimals and 10 is the
total number of digits (including decimals). Decimal precision can go to 24
places for a FLOAT.

 DOUBLE(M,D)—A double-precision floating-point number that cannot be
unsigned. You can define the display length (M) and the number of decimals
(D). This is not required and will default to 16,4, where 4 is the number of
decimals. Decimal precision can go to 53 places for a DOUBLE. REAL is a synonym
for DOUBLE.


DECIMAL(M,D)—An unpacked floating-point number that cannot be unsigned.
In unpacked decimals, each decimal corresponds to 1 byte. Defining the display
length (M) and the number of decimals (D) is required. NUMERIC is a synonym
for DECIMAL.
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