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https://dev.mysql.com/doc/refman/8.0/en/semijoins.html
This occurs due to heuristic pruning during greedy search, which can be avoided by setting optimizer_prune_level=0. The optimizer uses semijoin strategies to improve subquery execution, as described in this section. To list the classes that actually ... A semijoin is a preparation-time transformation that enables multiple execution strategies such as table pullout, duplicate weedout, first match, loose scan, and ...
https://dev.mysql.com/doc/refman/8.0/en/set.html
A consequence of this is that SET member values should not themselves contain commas. For example, you can retrieve numeric values from a SET column like this: mysql> SELECT set_col+0 FROM tbl_name; If a number is stored into a SET column, the bits ... A SET is a string object that can have zero or more values, each of which must be chosen from a list of permitted values specified when the table is ...
https://dev.mysql.com/doc/refman/8.0/en/sorted-index-builds.html
The drawbacks of this “top-down” method of building an index are the cost of searching for an insert position and the constant splitting and merging of B-tree nodes. This method of index creation is also known as a sorted index build. This ...
https://dev.mysql.com/doc/refman/8.0/en/spatial-geohash-functions.html
The functions in this section enable manipulation of geohash values, which provides applications the capabilities of importing and exporting geohash data, and of indexing and searching geohash values. Unless otherwise specified, functions in this ...
https://dev.mysql.com/doc/refman/8.0/en/storage-engines.html
NDB (also known as NDBCLUSTER): This clustered database engine is particularly suited for applications that require the highest possible degree of uptime and availability. Example: This engine serves as an example in the MySQL source code that ...
https://dev.mysql.com/doc/refman/8.0/en/stored-objects-security.html
This account must have the EXECUTE privilege for p1 as well as the UPDATE privilege for the table t1 referenced within the object body. In this case, the account “adopts” the object and, with the appropriate privileges, is able to execute it ...
https://dev.mysql.com/doc/refman/8.0/en/string-literals.html
This is true even for strings that are preceded by an introducer that indicates a different character set, as discussed in Section 12.3.6, “Character String Literal Character Set and Collation”. The \% and \_ sequences are used to search for ...
https://dev.mysql.com/doc/refman/8.0/en/tracing-example.html
row *************************** QUERY: SELECT SUM(alias2.col_varchar_nokey) AS c1, alias2.pk AS c2 FROM t1 AS alias1 STRAIGHT_JOIN t2 AS alias2 ON alias2.pk = alias1.col_int_key WHERE alias1.pk GROUP BY c2 ORDER BY alias1.col_int_key, alias2.pk This ...Now we can examine the trace, whose first column (QUERY), containing the original statement to be traced, is shown here: SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE\G ...
https://dev.mysql.com/doc/refman/8.0/en/using-spatial-indexes.html
The optimizer investigates whether available spatial indexes can be involved in the search for queries that use a function such as MBRContains() or MBRWithin() in the WHERE clause. | ...The following query finds all objects that are in the given ...
https://dev.mysql.com/doc/refman/8.0/en/with.html
WITH followed by WITH at the same level is not permitted, so this is illegal: WITH cte1 AS (...) WITH cte2 AS (...) SELECT ... This is illegal: WITH cte1 AS (...), cte1 AS (...) SELECT ... This constraint rules out mutually-recursive CTEs, where ...