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https://dev.mysql.com/doc/refman/8.4/en/create-table-generated-columns.html
If the column is also declared as NOT NULL, attempting to insert NULL is explicitly rejected with ER_BAD_NULL_ERROR. Generated column definitions have this syntax: col_name data_type [GENERATED ALWAYS] AS (expr) [VIRTUAL | STORED] [NOT NULL | NULL] ...Values of a generated column are computed from an expression included in the column ...
https://dev.mysql.com/doc/refman/8.4/en/example-auto-increment.html
For example: INSERT INTO animals (id,name) VALUES(0,'groundhog'); If the column is declared NOT NULL, it is also possible to assign NULL to the column to generate sequence numbers. For example: INSERT INTO animals (id,name) VALUES(NULL,'squirrel'); ...You can also explicitly assign 0 to the column to generate sequence numbers, unless the NO_AUTO_VALUE_ON_ZERO SQL mode is ...
https://dev.mysql.com/doc/refman/8.4/en/group-by-functional-dependence.html
A UNIQUE index over a NOT NULL column could be used instead of a primary key and the same functional dependence would apply. As with the previous example, a UNIQUE key over NOT NULL columns could be used instead of a primary key. If in the join ...
https://dev.mysql.com/doc/refman/8.4/en/information-schema-innodb-trx-table.html
TRX_REQUESTED_LOCK_ID The ID of the lock the transaction is currently waiting for, if TRX_STATE is LOCK WAIT; otherwise NULL. TRX_WAIT_STARTED The time when the transaction started waiting on the lock, if TRX_STATE is LOCK WAIT; otherwise NULL. The ...
https://dev.mysql.com/doc/refman/8.4/en/performance-schema-events-transactions-current-table.html
END_EVENT_ID This column is set to NULL when the event starts and updated to the thread current event number when the event ends. If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, ...The table stores one row per thread showing the current status of the thread's most recent monitored transaction event, so there is no system variable for configuring the table ...
https://dev.mysql.com/doc/refman/8.4/en/rewriter-query-rewrite-plugin-usage.html
row *************************** id: 1 pattern: SELECT ? pattern_database: NULL replacement: SELECT ? + 1 enabled: YES message: NULL pattern_digest: NULL normalized_pattern: NULL The rule specifies a pattern template indicating which SELECT ... To ...
https://dev.mysql.com/doc/refman/8.4/en/selecting-rows.html
As shown in the preceding section, it is easy to retrieve an entire table. But typically you don't want to see the entire table, particularly when it becomes large. Instead, you're usually more interested in answering a particular question, in ...
https://dev.mysql.com/doc/refman/8.4/en/show-events.html
row *************************** Db: myschema Name: e_daily Definer: jon@ghidora Time zone: SYSTEM Type: RECURRING Execute at: NULL Interval value: 1 Interval field: DAY Starts: 2018-08-08 11:06:34 Ends: NULL Status: ENABLED Originator: 1 ... SHOW ...
https://dev.mysql.com/doc/refman/8.4/en/tracing-example.html
(Observe that it could have a match, were the operator a null-safe equals <=>). Now we can examine the trace, whose first column (QUERY), containing the original statement to be traced, is shown here: SELECT * FROM ...
https://dev.mysql.com/doc/c-api/8.4/en/c-api-prepared-statement-data-structures.html
bool *is_null This member points to a bool variable that is true if a value is NULL, false if it is not NULL. For input, set *is_null to true to indicate that you are passing a NULL value as a statement parameter. is_null is a pointer to a boolean ... Prepared statements use several data structures: To obtain a statement handler, pass a MYSQL connection handler to mysql_stmt_init(), which returns a pointer to a MYSQL_STMT data ...