database management systems / DBMS - Page 2

PHP Fatal error: Uncaught mysqli_sql_exception: No database selected (SOLVED)

Posted by Alex On September 6, 2023

Let's look at a small PHP code that tries to connect to a MySQL or MariaDB DBMS and execute a query with a “SELECT” statement: <?php $db_user = "root"; $db_password = ""; $mysqli = new mysqli("localhost", $db_user, $db_password); if ($mysqli->connect_errno) { printf("Somehow we failed: %s\n", $mysqli->connect_error); exit(); } $query = "SELECT * FROM TestTABLE;"; $result = $mysqli->query($query); while ($row =...

“ERROR 1046 (3D000): No database selected” in MySQL and MariaDB (SOLVED)

Posted by Alex On September 3, 2023

How to fix “ERROR 1046 (3D000): No database selected” The error “ERROR 1046 (3D000): No database selected” occurs most often due to haste – of course, before performing actions with tables and the information stored in them, you must specify (that is, select to use) database. This simple mistake is a good reason to tell you about at least 5...

“ERROR 1366 (22007): Incorrect string value” in MySQL/MariaDB (SOLVED)

Posted by Alex On August 26, 2023

How to insert emoji into MySQL/MariaDB database On the one hand, inserting emoji into a MySQL / MariaDB database table does not require any special preparatory steps – just insert one or more emoji characters, which may contain other text. For example: INSERT INTO TestTABLE (`test_column`) VALUES ("?⏭️✈️ and hi ?"); But when executing the previous request, you may encounter...

PHP not displaying emoji from MySQL/MariaDB database (SOLVED)

Posted by Alex On August 25, 2023

When retrieving rows from a MySQL (MariaDB) database, you may encounter a situation where all the text is displayed correctly, but question marks are displayed instead of emoji. The most likely problem is an incorrectly used encoding when executing queries against the MySQL (MariaDB) DBMS. There are two ways to fix this situation. 1. Select utf8mb4_unicode_ci encoding when creating database...

What is the difference between utf8_general_ci, utf8_unicode_ci, utf8mb4_general_ci, utf8mb4_unicode_ci collations. Which collation, character set and encoding to choose for MySQL database

Posted by Alex On August 25, 2023

As of MySQL 5.5.3 you must use utf8mb4 and not utf8. Both of these groups refer to UTF-8 encoding, but the older utf8 has MySQL-specific restrictions that prevent characters above 0xFFFD from being used. Thus, neither utf8_general_ci nor utf8_unicode_ci need to be used anymore. As for the new encoding versions utf8mb4_general_ci and utf8mb4_unicode_ci. That is unicode preferred over general. The...

Error “ERROR 1142 (42000)”: command denied to user for table in MySQL / MariaDB (SOLVED)

Posted by Alex On August 25, 2023

Error number 1142 (42000) occurs when the user does not have enough privileges on the table or database to execute the query. An example of an error when executing a query with a SELECT statement: SELECT * FROM TestDB.TestTABLE; The request failed with an error: ERROR 1142 (42000): SELECT command denied to user 'mial'@'localhost' for table `TestDB`.`TestTABLE` An example of...

Error “ERROR 1143 (42000)”: command denied to user for column in table in MySQL (MariaDB) (SOLVED)

Posted by Alex On August 24, 2023

How to fix “ERROR 1143 (42000)” in MySQL (MariaDB) Error number 1143 (42000) occurs when a user has privileges on some columns of a table, but he tries to exercise his privileges on those columns for which he does not have permissions. If the user tries to perform actions for which he does not have privileges on any column in...

How to allow a MySQL (MariaDB) user to create new users and grant privileges to manage databases and their contents to other users

Posted by Alex On August 22, 2023

By default, the right (privilege) to create new users, as well as grant them rights to databases, is granted only to root. The root user can do all kinds of operations on databases and users. If you want to grant some administrative privileges to another user, then you can do so. How to create a MySQL (MariaDB) administrative user You...

Why is MySQL (MariaDB) asking for a password even when it is specified with the “-p” option (SOLVED)

Posted by Alex On August 21, 2023

If you are trying to connect to the MySQL (MariaDB) server on the command line, then you may have encountered the problem that the MySQL (MariaDB) client does not see the password. For example, when connecting to MariaDB using the command (where “USER” is the actual username and “PASSWORD” is the actual password): mariadb -u USER -p PASSWORD Instead of...

Why “mysql -h” doesn't show help. Error “option '-h' requires an argument” (SOLVED)

Posted by Alex On August 21, 2023

Perhaps the most popular command line option, regardless of the utility used, is the “-h” option. For most command-line programs, the “-h” option displays help on how to use the program. But if you try to get help for MySQL like this: mysql -h Then instead of the expected list of options and their values, you will get an error:...