④ date/time/datetime: date / time / date + time, without setting the length ③ float/double, floating-point data, storage of decimal places, length and reserved decimal places can be set, and the decimal places will be reserved automatically during insertion, but the and fixed decimal places in front of the decimal point cannot exceed the total length, eg: insert into floating double values (1.223456,2.454656), Saved data 1.223,2.45 varchar dynamically determines the length of the stored string according to the string we enter. ② varchar/char: char is the fixed length of the stored string. ① int/Integer, integer, length does not refer to the length of a number The most basic unit in the database is the table, which is used to store data (one table corresponds to one file) 1, MySQL 1. Common databases include oracle,sqlserver,mysql,DB2, database management system (DBMS) – > execute SQL – > operate database (disk file). Database (DataBaseManagement /DBMS) is a kind of database management system.
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