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VOOZH | about |
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VOOZH | about |
MySQL is an open-source, relational database management system (RDBMS) that uses Structured Query Language (SQL) to manage and manipulate data. It is one of the most popular database systems used in web applications, known for its speed, reliability, and ease of use. MySQL is commonly used in conjunction with programming languages such as PHP, Java, and Python to build dynamic websites and applications.
To create a database in MySQL, we can use the CREATE DATABASE statement followed by the name we want to give to our database. For example:
CREATE DATABASE mydatabase;Here’s a one-line summary for each MySQL string type:
You can add a User by using the CREATE command and specifying the necessary credentials. For example:
CREATE USER 'username'@'host' IDENTIFIED BY 'password';The default port for MySQL server is 3306. This is the port number used by MySQL to communicate with clients and other services by default, unless it is configured to use a different port in the MySQL configuration file (my.cnf or my.ini).
Batch mode in MySQL is used to execute a series of SQL queries from a file (often referred to as a batch file). The file contains multiple SQL statements that are executed in sequence. Here's the correct way to run MySQL in batch mode:
mysql -u username -p database_name < batch-file.sql
There are several storage engines in MySQL, and the table types depend on which storage engine is used. The common storage engines are:
Example:
SELECT LENGTH('Hello'); -- Returns 5 (1 byte per character in ASCII)
SELECT CHAR_LENGTH('Hello'); -- Returns 5 (5 characters)In the LIKE statement, the % and _ symbols are used for pattern matching:
%: Represents zero or more characters. It matches any sequence of characters, including an empty sequence._: Represents exactly one character. It matches any single character.Example:
SELECT * FROM Employees WHERE Name LIKE 'J%n';
SELECT * FROM Employees WHERE Name LIKE 'J_n'; There are 16 indexed columns can be created in a table.
There are six string types available for the column.
Example:
CREATE TABLE example (
float_value FLOAT,
double_value DOUBLE
);BLOB: Binary Large Object is used to store large amounts of binary data, such as images or files. The sorting and comparison of BLOB values are case-sensitive and done in binary format. Types:
TEXT: Used to store large amounts of text data. Unlike BLOB, TEXT data is case-insensitive and sorted lexicographically.
REGEXP (Regular Expression) is used in MySQL to perform pattern matching with string values. It allows you to use regular expressions for string searches within a query. The pattern can match anywhere in the string and is case-insensitive by default.
Syntax:
SELECT * FROM table_name WHERE column_name REGEXP 'pattern';
A column is a series of table cells that store a value for table's each row. we can add column by using ALTER TABLE statement.
ALTER TABLE tab_name
ADD COLUMN col_name col_definition [FIRST|AFTER exist_col];
We can remove columns in MySQL by using ALTER TABLE statement.
Syntax:
ALTERTABLE table_name DROPCOLUMN column1, column2....;
We can delete a table by using DROP TABLE statement. This statement deletes complete data of table.
DROP TABLE table-name;
mysql_fetch_array() Gets a result row as a related array or a regular array from database. mysql_fetch_object gets a result row as an object from the database.
The following query will be used to get top 10 rows.
SELECT * FROM table_name LIMIT 0,10;
current year, month, and date with hours, minutes, and seconds is shown by using NOW() command while CURRENT_DATE shows current year current month, and current date.
Syntax:
SELECT NOW();
SELECT CURRENT_DATE();
The DISTINCT keyword is used to remove duplicate rows from the result set, returning only unique values for the specified columns. The DISTINCT keyword is used with the SELECT statement.
Syntax:
SELECT DISTINCT colu1, colum2..
FROM table_name;
Storage engines are also called table types. Data is stored in a file using multiple techniques.
Below are some techniques.
To create a table in MySQL, the CREATE TABLE statement is used. Here's the syntax:
Syntax:
CREATE TABLE Employee (
Employee_Name VARCHAR(128),
Employee_ID VARCHAR(128),
Employee_Salary VARCHAR(16),
Designation CHAR(4)
);
We can add data to a table using the INSERT INTO statement.
Syntax:
INSERTINTO table_name ( field1, field2, field3 )
VALUES ( value1, value2, value3 );
The below statement is used to find duplicate rows.
SELECT Table_Name, Category
FROM Product
GROUP BY Name, Category
HAVING COUNT(id) > 1;
There are three types of relationships used in MySQL.
We can use INSERT statement to insert date in MySQL table. MySQL default date format is YYYY-MM-DD. Automatic MySQL consist many data types to store dates.
Syntax:
INSERTINTO table_name (column_name, column_date) VALUES ('DATE: Manual Date', '2023-5-20');
JOINs in MySQL are used to combine rows from two or more tables based on a related column. The most common types of joins are:
1. INNER JOIN: Returns records that have matching values in both tables.
SELECT * FROM table1
INNER JOIN table2 ON table1.id = table2.id;2. LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table and matched records from the right table. If there’s no match, NULL values are returned for the right table.
SELECT * FROM table1
LEFT JOIN table2 ON table1.id = table2.id;3. RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table and matched records from the left table. If there’s no match, NULL values are returned for the left table.
SELECT * FROM table1
RIGHT JOIN table2 ON table1.id = table2.id;4. FULL JOIN (MySQL does not support FULL JOIN natively): Returns all records when there is a match in either left (table1) or right (table2).
SELECT * FROM table1
LEFT JOIN table2 ON table1.id = table2.id
UNION
SELECT * FROM table1
RIGHT JOIN table2 ON table1.id = table2.id;A primary key in MySQL is a single field or a group of fields that are used to uniquely identify each record in a table. A primary key cannot be null or empty. ALTER TABLE statement is used to delete a primary key from a table.
Syntax:
ALTER TABLE table_name DROP PRIMARY KEY;
A heap table is usually used for temporary and fast temporary storage.
The primary key uniquely identified each row of a table. only one primary key is available for a table.
DELETE Command is used to delete rows from the table depending on given the condition. TRUNCATE command is used to DELETE all rows from the table. DELETE command is a Data Manipulation Language command. TRUNCATE command is a Data Definition Language command.
A SQL storage database is called InnoDB database. The InnoDB offers ACID transactions, row-level locking, and foreign key support. InnoDB is owned by Oracle Corporation.
During combining the results of more than one SELECT statement, the UNION operator deletes duplicate rows between the various SELECT statements. The UNION ALL also combines the result set of more than one SELECT statement, but it does not delete duplicate rows.
In MySQL, When a row is added to or updated in a table, a data type "timestamp" automatically records the time.
ENUM is a string object that can be used when creating tables to specify a set of predefined values.
CREATE table size(name ENUM('Small', 'Medium', 'Large');
MySQL config variable max_heap_table_size can be used to control the max size of heap.
Syntax:
SET max_heap_table_size = M
A database object that has no value is called view. Rows and columns exist in a view. A view is virtual table. it is created by combining one or more tables. The difference of a view and a table is that views are definition that build on other tables. If the underlying table changes, the View will also reflect those same changes.
Syntax:
CREATE VIEW view_name AS
SELECT columns
FROM tables
[WHERE conditions];
Every MyISAM table is stored on disk.
There are three storage formats can be used .
In MySQL, Blobs can be used to store images. All database images are first converted into blobs then saved and then they will be added to the database, and finally, it will later be stored on the disk.
A trigger is a procedural code in a database. Triggers are automatically triggered when specific events occur on a particular table. During column updating triggers are invoked automatically.
SIX triggers are available in MySQL table.
A list of permissions known as an Access Control List is connected to an object. It is MySQL server security model helps in troubleshooting issues like users being unable to connect. MySQL holds the ACL's cached in memory. ACL's also called grant tables. MySQL verifies the authentication data and permissions against the ACLs. It predetermined order whenever a user tries to log in or execute a command.
Normalization is used to avoid duplication and redundancy. it is a process of organizing data. There are many normal forms of normalization. which are also called successive levels. The first three regular forms are sufficient.
There are many options to create an index as below:
Cluster Index: An index type used to arrange data in a table is called a clustered index. The table's data are stored in a specific order based on the clustered index.
Non Cluster Index: A non-clustered index is also a type of index used to organize data in a table. The table's data are not stored in a specific order based on the non clustered index.
We can use the regular expressions function (REGEXP_LIKE) to validate emails. Below is the example of validate emails using a single query.
SELECT Email
FROM Vehicle
where NOT REGEXP_LIKE(Email, '[A-Z0-9._%+-]+@[A-Z0-9.-]+.[A-Z]{2,4}', 'i');
The MySQL Server is restricted from loading directories using the LOAD DATA INFILE command by the -secure-file-priv option. Use the SHOW VARIABLES LIKE "secure_file_priv" command to view the directory that has been configured.
There are two options to handle as below.