How to structure a MySQL Database with 50 variables per user? [duplicate]

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structuredatabase
90%

[43] The Memory engine in Percona Server supports variable-length rows.,MySQL sorts BLOB and TEXT columns differently from other types: instead of sorting the full length of the string, it sorts only the first max_sort_length bytes of such columns. If you need to sort by only the first few characters, you can either decrease the max_sort_length server variable or use ORDER BY SUBSTRING(column, length).,Create an empty table with exactly the same layout, except for the desired modification (such as added ENUM constants).,Before MySQL 5.0, BIT is just a synonym for TINYINT. But in MySQL 5.0 and newer, it’s a completely different data type with special characteristics. We discuss the new behavior here.

mysql > CREATE TABLE char_test(char_col CHAR(10));
mysql > INSERT INTO char_test(char_col) VALUES -
   > ('string1'), ('  string2'), ('string3 ');
mysql > SELECT CONCAT("'", char_col, "'") FROM char_test; +
-- -- -- -- -- -- -- -- -- -- -- -- -- -- +
|
CONCAT("'", char_col, "'") |
   + -- -- -- -- -- -- -- -- -- -- -- -- -- -- +
   |
   'string1' |
   |
   '  string2' |
   |
   'string3' |
   + -- -- -- -- -- -- -- -- -- -- -- -- -- -- +
mysql > SELECT CONCAT("'", varchar_col, "'") FROM varchar_test; +
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - +
|
CONCAT("'", varchar_col, "'") |
   + -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - +
   |
   'string1' |
   |
   '  string2' |
   |
   'string3 ' |
   + -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - +
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88%

To see the current set of optimizer flags, select the variable value: , To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section 27.12.14, “Performance Schema System Variable Tables”. , The character set used by the server for storing identifiers. The value is always utf8. , The server discards any result sets produced by statements in the value of init_connect.

To see the values that a server uses based on its compiled-in defaults and any option files that it reads, use this command:

mysqld--verbose--help
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72%

This makes the structure of new_table exactly like that of original_table, but DOES NOT copy the data. To copy the data, you'll need INSERT ... SELECT:,To inherit all table definitions, use the CREATE TABLE... LIKE syntax:,Note also that new_table inherits ONLY the basic column definitions, null settings and default values of the original_table. It does not inherit indexes and auto_increment definitions.,You can duplicate or "clone" a table's contents by executing a CREATE TABLE ... AS SELECT statement:

CREATE TABLE new_table AS SELECT * FROM original_table;
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65%

Data duplication happens because of many reasons. Finding duplicate values is one of the important tasks that you must deal with when working with the databases.,By using this query template, you can to find rows that have duplicate emails in the contacts table as follows:,For example, to find rows in the contacts table with duplicate values in first_name, last_name, and email column, you use the following query:,The find duplicate values in on one column of a table, you use follow these steps:

First, create a table named contacts with four columns: id, first_name, last_name, and email.

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      padding: 0 0.75 em;
      text - align: right; -
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CREATE TABLE contacts(
   id INT PRIMARY KEY AUTO_INCREMENT,
   first_name VARCHAR(50) NOT NULL,
   last_name VARCHAR(50) NOT NULL,
   email VARCHAR(255) NOT NULL
);
Code language: SQL(Structured Query Language)(sql)
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75%

When you create a database, make the data files as large as possible based on the maximum amount of data you expect in the database.,If the log files are available, the Database Engine uses those files instead of rebuilding the log files.,When ON is specified, the database can be the source or target of a cross-database ownership chain.,If you attach the database to the same server instance and version as the original database, no additional steps are required.

Syntax

CREATE DATABASE database_name[COLLATE collation_name]
   [;]

A simple example for creating a database.

CREATE DATABASE TestDB1;
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40%

By convention, server variables have usually been specified with an underscore in the configuration files, and a dash on the command line. You can however specify underscores as dashes - they are interchangeable.,Description: The version of the client/server protocol used by the MariaDB server. ,Depending on the ratio of actual available file handles, and table_open_cache size, the max. instance count may be auto adjusted to a lower value on server startup. ,Description: Time in seconds. If a thread takes longer than this to launch, the slow_launch_threads server status variable is incremented.

  • While in the mysql client, run:
SHOW VARIABLES;
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