General MySQL Oracle SQL Server

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SUM() - Total Value in Group
How to calculate the total value of a field expression in result set groups using the SUM() function? SUM(expr) is a MySQL built-in aggregate function that calculates the total value of a field expression in result set groups. For example: SELECT help_category_id, SUM(help_topic_id), COUNT(help_topi... 2023-12-01, 4322🔥, 0💬

Introduction to Date and Time Handling in MySQL
Where to find answers to frequently asked questions on Introduction to Date and Time Handling in MySQL? Here is a list of frequently asked questions and their answers compiled by FYIcenter.com DBA team on Introduction to Date and Time Handling in MySQL. Clear answers are provided with tutorial exerc... 2021-08-04, 4320🔥, 2💬

💬 2021-03-13 Strain John: Hey, u gave us good information. It is easy to understand for everyone and also having good content. I appreciated your afforts ...

Change Transaction Isolation Level in MySQL
How To View and Change the Current Transaction Isolation Level in MySQL? If you want to view or change the current transaction isolation level, you can use the following commands: SELECT @@TX_ISOLATION FROM DUAL; -- Viewing the current transaction isolation level. SET TRANSACTION ISOLATION LEVEL lev... 2017-08-08, 4252🔥, 0💬

UPDATE with Subquery Returning No Rows in MySQL
What Happens If the UPDATE Subquery Returns No Rows in MySQL? If you use a subquery to assign new values in the SET clause in an UPDATE statement, and the subquery returns no rows for an outer row, MySQL will provide a NULL value to the SET clause. The tutorial exercise below shows you a good exampl... 2018-01-08, 4242🔥, 0💬

Calculating the Difference between Two Time Values in MySQL
How To Calculate the Difference between Two Time Values in MySQL? If you have two time values, and you want to know the time difference between them, you can use the TIMEDIFF(time1, time2) function as shown below: SELECT TIMEDIFF(TIME('19:26:50'), TIME('09:26:50')) FROM DUAL; 10:00:00 SELECT TIMEDIF... 2017-12-26, 4217🔥, 0💬

Query Multiple Tables Jointly in MySQL
How To Query Multiple Tables Jointly in MySQL? If you want to query information stored in multiple tables, you can use the SELECT statement with a WHERE condition to make an inner join. Assuming that you have 3 tables in a forum system: "users" for user profile, "forums" for forums information, and ... 2017-06-23, 4187🔥, 0💬

Show Storage Engines Supported in MySQL in MySQL
How To See Which Storage Engines Are Supported in Your MySQL Server in MySQL? If you want to know exactly which storage engines are supported in your MySQL server, you can run the "SHOW ENGINES" command as shown in the tutorial example below: mysql&gt; SHOW ENGINES; +------------+---------+-----. .. 2017-08-08, 4067🔥, 0💬

PS_THREAD_ID() - PS Thread ID of Given Connect
How to obtain the performance schema thread id of a given connection using the PS_THREAD_ID() function? PS_THREAD_ID(con) is a MySQL built-in function that returns the performance schema thread id of a given connection. For example: SELECT CONNECTION_ID(); -- +-----------------+ -- | CONNECTION_ID()... 2025-02-16, 4061🔥, 0💬

Requirements for Using MySQL in PHP in MySQL
What Do You Need to Connect PHP to MySQL in MySQL? If you want to access MySQL database server in your PHP script, you need to make sure that a MySQL API module (extension) is installed and turned on in your PHP engine. PHP 5 now supports two MySQL API extensions: mysql - This is the standard MySQL ... 2017-07-30, 4052🔥, 0💬

CREATE Command Denied Error in MySQL
What Happens If You No CREATE Privilege in a Database in MySQL? In order to create tables in a database, your user account must have the CREATE privilege for that database. Otherwise you will get an error as shown in the following tutorial exercise: &gt;cd \mysql\bin &gt;mysql -u guest -ppub... 2018-03-10, 4046🔥, 0💬

USER() - Login Name of Current User
How to obtain the login name of the current user using the USER() function? USER() is a MySQL built-in function that returns the login name of the current user. Login name is defined as the combination of user name and the client IP address where you logged in from. For example: SELECT USER(); -- +-... 2025-01-07, 4036🔥, 0💬

INET6_NTOA() - IPv6 Address Number to String
How to convert an IPv6 address from number format to string using the INET6_NTOA() function? INET6_NTOA(int) is a MySQL built-in function that converts an IPv6 address from number format to string. For example: SET @ipv6 = UNHEX('FDFE0000000000005A55CAF FFEFA9089');SELECT HEX(@ipv6), INET6_NTOA(@ipv... 2026-02-02, 4021🔥, 0💬

Character String Data Types in MySQL
What Are Character String Data Types in MySQL? MySQL supports the following string data types: CHAR(n) same as CHARACTER(n) - Fixed width and " " padded characters strings. Default character set is ASCII. NCHAR(n) same as NATIONAL CHARACTER(n) - Fixed width and " " padded character strings with UTF8... 2018-04-12, 3975🔥, 0💬

Counting Duplicated Values in a Column in MySQL
How To Count Duplicated Values in a Column in MySQL? If you have a column with duplicated values, and you want to know what are those duplicated values are and how many duplicates are there for each of those values, you can use the GROUP BY ... HAVING clause as shown in the following example. It ret... 2017-10-16, 3962🔥, 0💬

Transaction Isolation Levels in MySQL
What Are Transaction Isolation Levels in MySQL? There are 4 transaction isolation levels defined by SQL-1992 standard: READ UNCOMMITTED - The SELECT statements in one transaction will read uncommitted data changes from transactions of all connected sessions. In this level, "dirty read" could happen,... 2017-08-03, 3961🔥, 0💬

Testing New User Account and Password in MySQL
How To Test a New User Account and Password in MySQL? If you have new user created with a password, you test it using "mysql" program with the "-u" and "-p" options. The following tutorial exercise shows you some interesting use cases of connecting to the server with user names and passwords: &g... 2017-09-08, 3925🔥, 0💬

CHARSET() - Detecting Character Set Name
How to detect the character set name associated to a given character string using the CHARSET() function? CHARSET(str) is a MySQL built-in function that returns the character set name associated to a given character string. A character set name refers to a set of rules to encode a set of characters ... 2025-10-24, 3883🔥, 0💬

"mysql" Command Line Arguments in MySQL
What Are the "mysql" Command Line Arguments in MySQL? "mysql" supports only one optional command line argument, "database". But "mysql" allows the operating system to redirect input and output streams at the command line level. Here are some good examples: "mysql databaseName" - Starts "mysql" in in... 2018-04-28, 3866🔥, 0💬

ROW_COUNT() - Affected Rows from Last DML Statement
How to obtain the affected row count from the last DML statement (INSERT, UPDATE or DELETE) using the ROW_COUNT() function? ROW_COUNT() is a MySQL built-in function that returns the affected row count from the last DML (Data Manipulation Language) statement (INSERT, UPDATE and DELETE). For example: ... 2025-02-16, 3841🔥, 0💬

UPDATEXML() - Updating Child Element in XML
How to update a child element in an XML document at a given location using the UPDATEXML() function? UPDATEXML(xml, path, subxml) is a MySQL built-in function that updates a child element in an XML document at a given location. For example: SET @xml = ' X Y '; SELECT UPDATEXML(@xml, '/a', ' Z '); +-... 2026-01-24, 3835🔥, 0💬

Converting Character Strings to Numeric Values in MySQL
How To Convert Character Strings to Numeric Values in MySQL? You can convert character strings to numeric values by using the CAST(string AS DECIMAL) or CAST(string AS SIGNED INTEGER) function as shown in the following examples: SELECT CAST('4123.45700' AS DECIMAL) FROM DUAL; 4123.46 -- Very poor co... 2018-03-28, 3835🔥, 0💬

MySQL Functions for Encryption and Compression
Where to find reference information and tutorials on MySQL database functions for Encryption and Compression? I want to know how to use COMPRESS(), ENCRYPT() and other related functions. Here is a collection of reference information and tutorials on MySQL database functions for Encryption and Compre... 2025-03-12, 3798🔥, 0💬

Running "mysql" Commands from a Batch File in MySQL
How To Run "mysql" Commands from a Batch File in MySQL? If you have group of "mysql" commands that need to be executed repeatedly, you can put them into a file, and run them from the file in "mysql" batch mode. Here is a batch file, \temp\links.sql, contains following commands: USE test; INSERT INTO... 2018-02-08, 3769🔥, 0💬

Connect to MySQL Server without Port Number in MySQL
How To Connect to a MySQL Server with Default Port Number in MySQL? If you want to connect a MySQL server with default port number, you can use the "mysql_connect($server)" function, where $server is the host name or IP address where the MySQL server is running. If successful, mysql_connect() will r... 2017-07-30, 3767🔥, 0💬

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General MySQL Oracle SQL Server