Unit-8 Introduction Of MySql

Types of table in PHP MySQL supports various of table types or storage engines to allow you to optimize your database. The table types are available in MySQL are: 1. ISAM 2. MyISAM 3. InnoDB 4. BerkeleyDB (BDB) 5. MERGE 6. HEAP

only MyISAM tables support indexing and searching feature. MyISAM is also the default table type when you create table without declaring which storage engine to use.

ISAM The original storage engine in MySQL was the ISAM engine. It was the only storage engine available until MySQL 3.23, when the improved MyISAM engine was introduced as the default. It is not available in MySQL 5.0. Embedded MySQL server versions do not support ISAM tables by default. Each ISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type. An.frm file stores the table definition. The data file has an.ISD extension. The index file has an.ISM extension.

MyISAM MyISAM table type is default when you create table. MyISAM table work very fast. The size of MyISAM table depends on the operating system and the data file are portable from system to system. With MyISAM table type, you can have 64 keys per table and maximum key length of 1024 bytes.

Each MyISAM table is stored on disk in three files. The files have names that begin with the table name and have an extension to indicate the file type. An.frm file stores the table format. The data file has an.MYD (MYData) extension. The index file has an.MYI (MYIndex) extension.

InnoDB Different from MyISAM table type, InnoDB table are transaction safe and supports row-level locking. Foreign keys are supported in InnoDB tables. The data file of InnoDB table can be stored in more than one file so the size of table depends on the disk space. Like the MyISAM table type, data file of InnoDB is portable from system to system. The disadvantage of InnoDB in comparison with MyISAM is it take more disk space.

BerkeleyDB (BDB) BDB is similar to InnoDB in transaction safe. It supports page level locking but data file are not portable.

MERGE Merge table type is added to treat multiple MyISAM tables as a single table so it remove the size limitation from MyISAM tables. When you create a MERGE table, MySQL creates two files on disk. The files have names that begin with the table name and have an extension to indicate the file type. An.frm file stores the table format, and an.MRG file contains the names of the underlying MyISAM tables that should be used as one.

HEAP Heap table is stored in memory so it is the fastest one. Because of storage mechanism, the data will be lost when the power failure and sometime it can reason the server run out of memory. Heap tables do not support columns with AUTO_INCREMENT and TEXT characteristics. The MEMORY storage engine associates each table with one disk file. The file name begins with the table name and has an extension of.frm to indicate that it stores the table definition.

QUERY IN MYSQL 1. SELECT SELECT selects records from the database. When this command is executed from the command line, MySQL prints all the records that match the query. The simplest use of SELECT is shown in this example: SELECT * FROM age information; The * means “show values for all fields in the table”; FROM specifies the table from which to extract the information.

2. INSERT For the table to be useful, we need to add information to it. We do so with the INSERT command: INSERT INTO age information (lastname, firstname, age) VALUES (´PATEL´, ´RAM´, 46); The syntax of the command is INSERT INTO, followed by the table in which to insert, a list within parentheses of the fields into which information is to be inserted, and the qualifier VALUES followed by the list of values in parentheses in the same order as the respective fields.

3.UPDATE Since the database is about people, information in it can change For instance, although a person’s birthday is static, their age changes. To change the value in an existing record, we can UPDATE the table. Let’s say the fictional Larry Wall has turned 47: UPDATE age information SET age = 47 WHERE lastname = ´PATEL´; Be sure to use that WHERE clause; otherwise, if we had only entered UPDATE age information SET age = 47, all the records in the database would have been given the age of 47!

4. DELETE Sometimes we need to delete a record from the table This is done with the DELETE command. DELETE FROM age information WHERE lastname = ´PATEL´;

TRUNCATE TRUNCATE tbl_name TRUNCATE TABLE empties a table completely. Logically, this is equivalent to a DELETE statement that deletes all rows, but there are practical differences under some circumstances.DELETE TRUNCATE `student` That is, we want to keep the layout and structure of the table, but just empty the data. MySQL has a handy command for emptying a table known as TRUNCATE.

Alias To save typing and add additional functionality, table aliases are sometimes used in queries. Consider an example that finds all inventory details of wine #183: SELECT * FROM inventory i, wine w WHERE i.wine_id = 183 AND i.wine_id = w.wine_id; In this query, the FROM clause specifies aliases for the table names. The alias inventory i means than the inventory table can be referred to as i elsewhere in the query. For example, i.wine_id is the same as inventory.wine_id. This saves typing in this query.

Order By Suppose we have a large amount of data in a database. When we perform a SELECT query on the data, we get a whole bunch of data. Now suppose we wanted to sort that data, that is, we wanted to arrange the data in alphabetical order before showing it to a user in their browser. Would we sort the data using PHP? Of course not. MySQL has its own built-in sorting engine and we can invoke it using order by in our SQL.

If we had the table "employees" and we wanted to output the entire table sorting in ascending order by last name we would use the following code: SELECT * FROM employees ORDER BY last_name ASC; If we wanted to sort in descending order we would use: SELECT * FROM employees ORDER BY last_name DESC; If we do not specify "ASC" or "DESC", MySQL will default to "ASC" or ascending.

Difference Between Truncate and Delete TRUNCATE is a DDL (data definition language) command whereas DELETE is a DML (data manipulation language) command. You can use WHERE clause(conditions) with DELETE but you can't use WHERE clause with TRUNCATE. You cann't rollback data in TRUNCATE but in DELETE you can rollback data.TRUNCATE removes(delete) the record permanently. A trigger doesn’t get fired in case of TRUNCATE whereas Triggers get fired in DELETE command. If tables which are referenced by one or more FOREIGN KEY constraints then TRUNCATE will not work. Delete and Truncate both are logged operation. But DELETE is a logged operation on a per row basis and TRUNCATE logs the deallocation of the data pages in which the data exists. TRUNCATE is faster than DELETE.