General MySQL Oracle SQL Server

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UNCOMPRESS() - Uncompressing Data
How to uncompress (restore) compressed data using the UNCOMPRESS() function? UNCOMPRESS(str) is a MySQL built-in function that uncompresses a given compressed byte string using the default LZ77 compression algorithm. For example: SELECT UNCOMPRESS(x'37000000789C738BF 44C4ECD2B492DD24BCECFD57123960 700... 2024-12-18, 3057🔥, 0💬

Close MySQL Connection Objects in MySQL
How To Close MySQL Connection Objects in MySQL? MySQL connection objects created with mysql_connect() calls should be closed as soon as you have finished all of your database access needs by calling mysql_close($con) function. This will reduce the consumption of connection resources on your MySQL se... 2017-11-11, 3053🔥, 0💬

Sorting Output in Descending Order in MySQL
How To Sort Output in Descending Order in MySQL? If you want to sort a column in descending order, you can specify the DESC keyword in the ORDER BY clause. The following SELECT statement first sorts the "tag" in descending order, then sorts the "counts" in ascending order: mysql&gt; SELECT tag, ... 2017-11-02, 3053🔥, 0💬

What Is Binary Log File in MySQL
What Is Binary Log File in MySQL? MySQL server binary log file plays an important role in restoring database changes to the server. Main features on binary log files are: Binary logs can be turned on by "--log-bin=fileBaseName" option on "mysqld". Binary logs only records statements that are changin... 2017-11-29, 3052🔥, 0💬

Using Subqueries with the EXISTS Operator in MySQL
How To Use Subqueries with the EXISTS Operator in MySQL? A subquery can be used with the EXISTS operator as "EXISTS (subquery)", which returns true if the subquery returns one or more rows. The following statement is a good example of "EXISTS (subquery)". It returns rows from fyi_links table that th... 2017-09-17, 3051🔥, 0💬

What Are DML Statements in MySQL
What Are DML Statements in MySQL? DML (Data Manipulation Language) statements are statements to change data values in database tables. The are 3 primary DML statements: INSERT - Inserting new rows into database tables. UPDATE - Updating existing rows in database tables . DELETE - Deleting existing r... 2018-01-24, 3050🔥, 0💬

Data File of BDB Storage Engine in MySQL
Where Table Data Is Stored by the BDB Storage Engine in MySQL? By default, MySQL provides \mysql\data directory for all storage engines to store table data. Under \mysql\data directory, the BDB storage engine will create one file for each table to store table data and index data. If a new table is c... 2017-08-13, 3049🔥, 0💬

What Is Index in MySQL
What Is Index in MySQL? An index is a single column or multiple columns defined to have values pre-sorted to speed up data retrieval speed.   ⇒ What Is View in MySQL ⇐ What Is Foreign Key in MySQL ⇑ Database Basics and Terminologies in MySQL ⇑⇑ MySQL Database Tutorials 2017-07-07, 3049🔥, 0💬

Creating a New Table in MySQL
How To Create a New Table in MySQL? If you want to create a table, you can run the CREATE TABLE statement as shown in the following sample script: &lt;?php include "mysql_connection.php"; $sql = "CREATE TABLE fyi_links (" . " id INTEGER NOT NULL" . ", url VARCHAR(80) NOT NULL" . ", notes VARCHAR... 2017-10-08, 3048🔥, 0💬

What Are Group Functions in MySQL
What Are Group Functions in MySQL? Group functions are functions applied to a group of rows. Examples of group functions are: COUNT(*) - Returns the number of rows in the group. MIN(exp) - Returns the minimum value of the expression evaluated on each row of the group. MAX(exp) - Returns the maximum ... 2018-01-06, 3047🔥, 0💬

Build WHERE Criteria with Web Form Data in MySQL
How To Build WHERE Criteria with Web Form Search Fields in MySQL? If your PHP script is linked to a Web form which takes search key words for multiple data fields. For example, your Web form asks your visitor to search for Website links with a URL search field, a Website title search field, a descri... 2017-06-23, 3043🔥, 0💬

Using Group Functions in the ORDER BY Clause in MySQL
Can Group Functions Be Used in the ORDER BY Clause in MySQL? If the query output is aggregated as groups, you can sort the groups by using group functions in the ORDER BY clause. The following statement returns how many links were created in each year in each tag. The group output is sorted by the c... 2017-12-31, 3042🔥, 0💬

Define the ID Column as Auto-Incremented in MySQL
How To Define the ID Column as Auto-Incremented in MySQL? Many tables require an ID column to assign a unique ID number for each row in the table. For example, if you have a table to hold forum member profiles, you need an ID number to identify each member. To allow MySQL server to automatically ass... 2017-09-12, 3042🔥, 0💬

Violation of Unique Value Constraint in MySQL
What Happens If Unique Value Constraints Are Violated in MySQL? If you are inserting a new record that has values violating a unique constraint, you will get an error. Note that primary key column has a unique value constraint by default. The following tutorial exercise gives you some good examples:... 2018-01-16, 3041🔥, 0💬

CREATE TABLE Statement in MySQL
How To Create a New Table in MySQL? If you want to create a new table, you can use the "CREATE TABLE" statement. The following tutorial script shows you how to create a table called "tip": mysql&gt; CREATE TABLE tip (id INTEGER PRIMARY KEY, subject VARCHAR(80) NOT NULL, description VARCHAR(256) ... 2018-03-10, 3035🔥, 0💬

Selecting Columns in a Query in MySQL
How To Select Some Columns from a Table in MySQL? If you want explicitly tell the query to return some columns, you can specify the column names in the SELECT clause. The following select statement returns only two columns, "id" and "url" from the table "fyi_links": mysql&gt; SELECT id, url FROM... 2017-11-05, 3035🔥, 0💬

VALIDATE_PASSWORD_STRENGTH() - Password Strength Test
How to test the strength of a password using the VALIDATE_PASSWORD_STRENGTH() function? VALIDATE_PASSWORD_STRENGTH(pas sword)is a MySQL built-in function that calculates the strength of a given password. It requires validate_password plugin component to be installed. For example: SELECT VALIDATE_PAS... 2024-12-18, 3033🔥, 0💬

Rename an Existing Table in MySQL
How To Rename an Existing Table in MySQL? If you want to rename an existing table, you can use the "ALTER TABLE ... RENAME TO" statement. The tutorial script below shows you a good example: mysql&gt; ALTER TABLE tip RENAME TO faq; Query OK, 0 rows affected (0.01 sec) mysql&gt; SELECT * FROM ... 2018-02-14, 3033🔥, 0💬

JSON_SCHEMA_VALID() - JSON Schema Validation
How to validate a JSON value against a JSON schema using the JSON_SCHEMA_VALID() function? JSON_SCHEMA_VALID(schema, json) is a MySQL built-in function that validates a JSON value against a given JSON schema. For example: SET @schema = '{ "id": "http://json-schema.org/geo", "$schema": "http://json-s... 2024-11-23, 3031🔥, 0💬

Experiment with Dead Locks in MySQL
How To Experiment Dead Locks in MySQL? If you want to have some experience with dead locks, you can create two windows running two mysql transactions in two sessions at the REPEATABLE READ transaction isolation level. Then run some UPDATE statements as shown in the tutorial exercise below: (session ... 2017-07-21, 3029🔥, 0💬

What Is InnoDB in MySQL
What Is InnoDB in MySQL? InnoDB is a transaction safe storage engine developed by Innobase Oy (an Oracle company now).   ⇒ What Is BDB in MySQL ⇐ What Is MyISAM in MySQL ⇑ Database Basics and Terminologies in MySQL ⇑⇑ MySQL Database Tutorials 2017-07-03, 3029🔥, 0💬

Retrieving the Last Sequence ID in MySQL
How To Get the Last ID Assigned by MySQL in MySQL? If you use an ID column with AUTO_INCREMENT attribute, you can use the mysql_insert_id() function to get the last ID value assigned by the MySQL server, as shown in the sample script below: &lt;?php include "mysql_connection.php"; $sql = "INSERT... 2017-09-12, 3028🔥, 0💬

Number of Rows Selected or Affected in MySQL
How To Get the Number of Rows Selected or Affected by a SQL Statement in MySQL? There are two functions you can use the get the number of rows selected or affected by a SQL statement: mysql_num_rows($res) - Returns the number of rows selected in a result set object returned from SELECT statement. my... 2017-10-08, 3025🔥, 0💬

Turn on Binary Logs in MySQL
How To Turn on Binary Logs in MySQL? If you want MySQL to write binary logs to a file, you can use the "--log-bin=fileBaseName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option: &gt;cd \mysql\bin &gt;mkdir \mysql\logs &gt... 2017-11-29, 3024🔥, 0💬

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General MySQL Oracle SQL Server