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https://dev.mysql.com/doc/refman/5.7/en/flow-control-functions.html
mysql> SELECT IF(1>2,2,3); -> 3 mysql> SELECT IF(1<2,'yes','no'); -> 'yes' mysql> SELECT IF(STRCMP('test','test1'),'no','yes'); -> 'no' IFNULL(expr1,expr2) If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2. mysql> SELECT ...
https://dev.mysql.com/doc/refman/5.7/en/group-by-functional-dependence.html
The following discussion provides several examples of the ways in which MySQL detects functional dependencies. The examples use this notation: {X} -> {Y} Understand this as “X uniquely determines Y,” which also means that Y is functionally ...
https://dev.mysql.com/doc/refman/5.7/en/information-schema-optimization.html
For example, if you are selecting from TABLES, using a constant lookup value for TABLE_SCHEMA in the WHERE clause enables a data directory scan to be avoided. Example: SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'test'; Use ... Applications that monitor databases may make frequent use of INFORMATION_SCHEMA ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-compression-tuning.html
\! ls -l data/test/big_table.ibd CREATE TABLE key_block_size_4 LIKE big_table; ALTER TABLE key_block_size_4 key_block_size=4 row_format=compressed; INSERT INTO key_block_size_4 SELECT * FROM big_table; commit; -- Check how much space is needed for a ... Most often, the internal optimizations described in InnoDB Data Storage and Compression ensure that the system runs well with compressed ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-transaction-isolation-levels.html
This means that if you issue several plain (nonlocking) SELECT statements within the same transaction, these SELECT statements are consistent also with respect to each other. For locking reads (SELECT with FOR UPDATE or LOCK IN SHARE MODE), UPDATE, ... Transaction isolation is one of the foundations of database ...
https://dev.mysql.com/doc/refman/5.7/en/lock-tables.html
You must have the LOCK TABLES privilege, and the SELECT privilege for each object to be locked. For example, in the following set of statements, UNLOCK TABLES releases the global read lock but does not commit the transaction because no table locks ... LOCK {TABLE | TABLES} tbl_name [[AS] alias] lock_type [, tbl_name [[AS] alias] lock_type] ...
https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-limitations-transactions.html
To ensure that a given transaction reads only before or after values, you can impose row locks using SELECT ... This can be done by using the IGNORE INDEX index hint as part of the SELECT statement reading the table (see Section 8.9.4, “Index ...
https://dev.mysql.com/doc/refman/5.7/en/partitioning-handling-nulls.html
Partitioning in MySQL does nothing to disallow NULL as the value of a partitioning expression, whether it is a column value or the value of a user-supplied expression. Even though it is permitted to use NULL as the value of an expression that must ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-statement-digests.html
Consider these statements: SELECT * FROM orders WHERE customer_id=10 AND quantity>20 SELECT * FROM orders WHERE customer_id = 20 AND quantity > 100 To normalize these statements, the parser replaces data values by ? and adjusts whitespace. Both ...
https://dev.mysql.com/doc/refman/5.7/en/stored-objects-security.html
The invoker must have appropriate privileges to reference the object (for example, EXECUTE to call a stored procedure or SELECT to select from a view), but during object execution, the invoker's privileges are ignored and only the DEFINER account ...