What are the other commands to know the structure of table using MySQL commands except explain command?

The Describe command in MySQL allows we to show all the fields in a table, the field's name, data type, as well as additional information, such as whether it is Null, Key, and Default.

 

So, to examine all the information in a table, so you can see all the fields and data types of each field, along with other information, such as Null, Key, Default, you can use the command line:

Describe table_name

This will show all the structural information of a table.

If we have actually inserted data into the table, the data will not show up when using the Describe function. The Describe function only shows the table structure, not the actual data inside.

DESCRIBE provides information about the columns in a table.

It is a shortcut for SHOW COLUMNS FROM.

col_name can be a column name, or a string containing the SQL “%” and “_” wildcard characters to obtain output only for the columns with names matching the string. There is no need to enclose the string within quotation marks unless it contains spaces or other special characters.

The description for SHOW COLUMNS provides more information about the output columns.

If the data types differ from what we expect them to be based on a CREATE TABLE statement, MySQL sometimes changes data types when we create or alter a table. The DESCRIBE statement is provided for compatibility with Oracle.

What is maximum size of a database in mysql?

If the operating system or filesystem places a limit on the number of files in a directory, MySQL is bound by that constraint. The efficiency of the operating system in handling large numbers of files in a directory can place a practical limit on the number of tables in a database. If the time required to open a file in the directory increases significantly as the number of files increases, database performance can be adversely affected.
The amount of available disk space limits the number of tables.
MySQL 3.22 had a 4GB (4 gigabyte) limit on table size. With the MyISAM storage engine in MySQL 3.23, the maximum table size was increased to 65536 terabytes (2567 – 1 bytes). With this larger allowed table size, the maximum effective table size for MySQL databases is usually determined by operating system constraints on file sizes, not by MySQL internal limits.
The InnoDB storage engine maintains InnoDB tables within a tablespace that can be created from several files. This allows a table to exceed the maximum individual file size. The tablespace can include raw disk partitions, which allows extremely large tables. The maximum tablespace size is 64TB.
The following table lists some examples of operating system file-size limits. This is only a rough guide and is not intended to be definitive. For the most up-to-date information, be sure to check the documentation specific to your operating system.
Operating System File-size Limit
Linux 2.2-Intel 32-bit 2GB (LFS: 4GB)
Linux 2.4+ (using ext3 filesystem) 4TB
Solaris 9/10 16TB
NetWare w/NSS filesystem 8TB
Win32 w/ FAT/FAT32 2GB/4GB
Win32 w/ NTFS 2TB (possibly larger)
MacOS X w/ HFS+ 2TB

How can we find the number of rows in a table using MySQL?

Counting Rows

SELECT COUNT(*) FROM... WHERE...

 

Or, the alternative:

SELECT 1 FROM... WHERE...

 

// and then count the results with a built-in function, e.g. in PHP mysql_num_rows()

 

We can get the number of rows or records present in a table by using mysql_num_rows() function. This function is to be used along with mysql select query. We can add condition by using mysql where clause to the select query and get the conditional rows. This function is widely used in different php scripts.

 

This can't be used along with update, delete, insert commands, for this mysql_affected_rows is to be used. You can use count command also to read the number of records. Here is the sample code for mysql_num_rows():

 

$query = mysql_query("SELECT * FROM student");

$number=mysql_num_rows($query);

echo "Total records in Student table= ". $number;