The operator precedence of the MySQL database is as follows (from high to low):
- brackets()
- Multiplication*, division/, modulo %
- Addition +, Subtraction -
- Comparison operators: =, >, <, >=, <=, <>
- logical NOT
- Logic and AND
- logical OR
Commonly used MySQL functions include:
- Character functions: CONCAT, LENGTH, SUBSTRING, REPLACE, UPPER, LOWER, etc.
- Numerical functions: ABS, ROUND, CEILING, FLOOR, RAND, etc.
- Date and time functions: CURDATE, NOW, DATE_ADD, DATEDIFF, DATE_FORMAT, etc.
- Aggregate functions: SUM, COUNT, AVG, MIN, MAX, etc.
- Conditional functions: IF, CASE WHEN, COALESCE, etc.
- String functions: LIKE, INSTR, TRIM, SPLIT_STR, etc.
- Mathematical functions: POW, SQRT, MOD, EXP, etc.
Understanding of MySQL transactions and indexes:
A transaction is a set of database operations that are treated as a single logical unit of work. Transactions have the characteristics of atomicity, consistency, isolation, and durability (ACID). In a transaction, either all operations are successfully executed and committed, or failure of any operation will cause the transaction to roll back to the original state.
Transactions can be managed using the BEGIN, COMMIT, and ROLLBACK statements. BEGIN begins a new transaction, COMMIT commits the transaction and makes its results permanent, and ROLLBACK cancels the transaction and undoes operations already performed.
An index is a data structure used in a database to improve query efficiency. They speed up finding and sorting data. MySQL supports various types of indexes, including B-Tree indexes, hash indexes, full-text indexes, etc.
In MySQL, indexes can be created with the CREATE INDEX statement and dropped with the DROP INDEX statement. Indexes can be used to speed up retrieval of WHERE clauses, but also increase the overhead of insert, update, and delete operations.
Proper use of transactions and indexes can improve database performance and data consistency. Transactions can ensure the atomicity and consistency of multiple operations, and indexes can speed up query operations, but the cost of creating and maintaining indexes needs to be weighed.