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https://dev.mysql.com/doc/refman/5.7/en/enterprise-encryption-functions.html
If the arguments are not suitable to permit a function to perform the requested operation, it returns NULL or 0 as appropriate. This occurs, for example, if a function does not support a specified algorithm, a key length is too short or long, or a ... MySQL Enterprise Encryption functions have these general characteristics: For arguments of the wrong type or an incorrect number of arguments, each function returns an ...
https://dev.mysql.com/doc/refman/5.7/en/case.html
The CASE statement cannot have an ELSE NULL clause, and it is terminated with END CASE instead of END. This syntax cannot be used to test for equality with NULL because NULL = NULL is false. CASE case_value WHEN when_value THEN statement_list [WHEN ...
https://dev.mysql.com/doc/refman/5.7/en/merge-storage-engine.html
The column of the underlying table and the MERGE table can be NULL. The MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. “Identical” means that all tables have ...
https://dev.mysql.com/doc/refman/5.7/en/getting-information.html
To find out which database is currently selected, use the DATABASE() function: mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+ If you have not yet selected any database, the result is NULL. What ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-events-table.html
If the event's timing is determined by an EVERY clause instead of an AT clause (that is, if the event is recurring), the value of this column is NULL. This is displayed as a DATETIME value, and is NULL if no start date and time are defined for the ... The EVENTS table provides information about Event Manager events, which are discussed in Section 23.4, “Using the Event ...
https://dev.mysql.com/doc/refman/5.7/en/constraint-invalid-data.html
For strings, MySQL stores either the empty string or as much of the string as can be stored in the column. If you try to store a string that does not start with a number into a numeric column, MySQL Server stores 0. If you try to store NULL into a ... MySQL 5.7.5 and later uses strict SQL mode by default, which treats invalid values such that the server rejects them and aborts the statement in which they occur (see Section 5.1.10, “Server SQL ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-row-format.html
An SQL NULL value reserves one or two bytes in the record directory. An SQL NULL value reserves zero bytes in the data part of the record if stored in a variable-length column. Reserving fixed space for NULL values permits columns to be updated in ... The row format of a table determines how its rows are physically stored, which in turn can affect the performance of queries and DML ...
https://dev.mysql.com/doc/refman/5.7/en/flow-control-functions.html
mysql> SELECT IFNULL(1,0); -> 1 mysql> SELECT IFNULL(NULL,10); -> 10 mysql> SELECT IFNULL(1/0,10); -> 10 mysql> SELECT IFNULL(1/0,'yes'); -> 'yes' The default return type of IFNULL(expr1,expr2) is the more “general” of the two expressions, in ...
https://dev.mysql.com/doc/refman/5.7/en/gis-geometrycollection-property-functions.html
If any argument is NULL or the geometry argument is an empty geometry, the return value is NULL. mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))'; mysql> SELECT ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)); ...GeometryN() is ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting-datadict.html
Information about table definitions is stored both in the .frm files, and in the InnoDB data dictionary. If you move .frm files around, or if the server crashes in the middle of a data dictionary operation, these sources of information can become ...