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https://dev.mysql.com/doc/refman/5.7/en/charset-unicode-utf8mb3.html
For example: mysqld --character-set-server=utf8mb3 SET NAMES 'utf8mb3'; /* and other SET statements that have similar effect */ SELECT _utf8mb3 'a'; For information about data type storage as it relates to multibyte character sets, see String Type ... The utf8mb3 character set has these characteristics: Supports BMP characters only (no support for supplementary characters) Requires a maximum of three bytes per multibyte ...
https://dev.mysql.com/doc/refman/5.7/en/comparisons-using-subqueries.html
WHERE 'a' = (SELECT column1 FROM t1) MySQL also permits this construct: non_subquery_operand LIKE (subquery) At one time the only legal place for a subquery was on the right side of a comparison, and you might still find some old DBMSs that insist ... The most common use of a subquery is in the form: non_subquery_operand comparison_operator (subquery) Where comparison_operator is one of these operators: = > < >= <= <> != <=> For example: ...
https://dev.mysql.com/doc/refman/5.7/en/concurrent-inserts.html
If there are multiple INSERT statements, they are queued and performed in sequence, concurrently with the SELECT statements. In addition, for those statements a read lock is placed on the selected-from table such that inserts into that table are ...
https://dev.mysql.com/doc/refman/5.7/en/condition-filtering.html
To the extent that the optimizer can use information about conditions on rows selected from one table and passed to the next, the more accurately it can compute row estimates and choose the best execution plan. Without condition filtering, the ...
https://dev.mysql.com/doc/refman/5.7/en/engine-condition-pushdown-optimization.html
This optimization improves the efficiency of direct comparisons between a nonindexed column and a constant. In such cases, the condition is “pushed down” to the storage engine for evaluation. This optimization can be used only by the NDB ...
https://dev.mysql.com/doc/refman/5.7/en/enum.html
This means that you can use the following SELECT statement to find rows into which invalid ENUM values were assigned: mysql> SELECT * FROM tbl_name WHERE enum_col=0; The index of the NULL value is NULL. For example, you can retrieve numeric values ... An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation ...
https://dev.mysql.com/doc/refman/5.7/en/example-maximum-column-group-row.html
Task: For each article, find the dealer or dealers with the most expensive price. Other possibilities for solving the problem are to use an uncorrelated subquery in the FROM clause or a LEFT JOIN.
https://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html
To investigate database page corruption, you might dump your tables from the database with SELECT ... Serious corruption might cause SELECT * FROM tbl_name statements or InnoDB background operations to unexpectedly exit or assert, or even cause ...
https://dev.mysql.com/doc/refman/5.7/en/fulltext-search-mecab.html
SELECT COUNT(*) FROM articles WHERE MATCH(title,body) AGAINST('データベース管理' IN NATURAL LANGUAGE MODE); For boolean mode search, the search term is converted to a search phrase. SELECT COUNT(*) FROM articles WHERE MATCH(title,body) ...
https://dev.mysql.com/doc/refman/5.7/en/generated-column-index-optimizations.html
You can see this using EXPLAIN: mysql> EXPLAIN SELECT * FROM t1 WHERE f1 + 1 > 9\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: t1 partitions: NULL type: range possible_keys: gc key: gc key_len: 5 ...For example: CREATE TABLE t1 (f1 INT, gc INT AS (f1 + 1) STORED, INDEX (gc)); The generated column, gc, is defined as the expression f1 + ...