面试题与答案

SQL (Structured Query Language) is a domain-specific language used for managing and manipulating relational databases.

SQL is a language, whereas MySQL is a relational database management system that uses SQL as its query language.

A primary key is a unique identifier for a record in a table. It must contain unique values and cannot be NULL.

An index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space.

A foreign key is a column or a set of columns in a table that refers to the primary key of another table, establishing a link between the two tables.

SELECT COUNT(*) FROM table;

A view is a virtual table based on the result of a SELECT query, and it does not store the data itself.

Example:

CREATE VIEW view_name AS SELECT column1, column2 FROM table WHERE condition;

UPDATE table SET column1 = value1, column2 = value2 WHERE condition;

The ORDER BY clause is used to sort the result set of a query in ascending or descending order based on one or more columns.

Example:

SELECT column1, column2 FROM table ORDER BY column1 DESC;

SELECT * FROM table ORDER BY timestamp_column DESC LIMIT 1;

CHAR is a fixed-length string data type, while VARCHAR is a variable-length string data type. CHAR pads spaces to the maximum length, while VARCHAR only stores the actual data without padding.

The DISTINCT keyword is used to return unique values in the result set of a SELECT query by eliminating duplicate rows.

Example:

SELECT DISTINCT column FROM table;

The UPDATE statement is used to modify the existing records in a table by changing the values of one or more columns.

Example:

UPDATE table SET column1 = value1, column2 = value2 WHERE condition;

The LIKE operator is used to search for a specified pattern in a column. It is often used with wildcard characters (% and _).

Example:

SELECT * FROM table WHERE column LIKE 'pattern%';

SELECT * FROM table ORDER BY column DESC LIMIT N;