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https://dev.mysql.com/group-by-optimization.html
For example, with c1 VARCHAR(20), INDEX (c1(10)), the index uses only a prefix of c1 values and cannot be used for Loose Index Scan. The most general way to satisfy a GROUP BY clause is to scan the whole table and create a new temporary table where ...
https://dev.mysql.com/information-functions.html
It may be used to time how quickly MySQL processes the expression. The result value is 0, or NULL for inappropriate arguments such as a NULL or negative repeat count. The intended use is from within the mysql client, which reports query execution ...
https://dev.mysql.com/information-schema-introduction.html
The definition for character columns (for example, TABLES.TABLE_NAME) is generally VARCHAR(N) CHARACTER SET utf8 where N is at least 64. INFORMATION_SCHEMA provides access to database metadata, information about the MySQL server such as the name of ...
https://dev.mysql.com/innodb-auto-increment-handling.html
To make this clear, consider an example that uses this table: CREATE TABLE t1 ( c1 INT(11) NOT NULL AUTO_INCREMENT, c2 VARCHAR(10) DEFAULT NULL, PRIMARY KEY (c1) ) ENGINE=InnoDB; Suppose that there are two transactions running, each inserting rows ... InnoDB provides a configurable locking mechanism that can significantly improve scalability and performance of SQL statements that add rows to tables with AUTO_INCREMENT ...
https://dev.mysql.com/innodb-compression-tuning.html
Character strings often compress well, whether defined in CHAR, VARCHAR, TEXT or BLOB columns. Most often, the internal optimizations described in InnoDB Data Storage and Compression ensure that the system runs well with compressed data. However, ...
https://dev.mysql.com/innodb-compression-usage.html
This setting may still be useful for tables with many long BLOB, VARCHAR or TEXT columns, because such values often do compress well, and might therefore require fewer overflow pages as described in Section 15.9.1.5, “How Compression Works for ...
https://dev.mysql.com/innodb-file-per-table-tablespaces.html
A file-per-table tablespace contains data and indexes for a single InnoDB table, and is stored on the file system in its own data file. File-per-table tablespace characteristics are described under the following topics in this section: ...
https://dev.mysql.com/innodb-ft-index-cache-table.html
The INNODB_FT_INDEX_CACHE table provides token information about newly inserted rows in a FULLTEXT index. Before querying it, set the value of the innodb_ft_aux_table system variable to the name (including the database name) of the table that ...
https://dev.mysql.com/innodb-ft-index-table-table.html
The INNODB_FT_INDEX_TABLE table provides information about the inverted index used to process text searches against the FULLTEXT index of an InnoDB table. Before querying it, set the value of the innodb_ft_aux_table system variable to the name ...
https://dev.mysql.com/innodb-information-schema-fulltext_index-tables.html
INNODB_FT_BEING_DELETED: Provides a snapshot of the INNODB_FT_DELETED table; it is used only during an OPTIMIZE TABLE maintenance operation. When OPTIMIZE TABLE is run, the INNODB_FT_BEING_DELETED table is emptied, and DOC_ID values are removed from ...
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