How to create a table and what to look for in a design table

1, table: is the database used to store data to understand the object, is a collection of structured data, is the basis of the entire database system. The concept of everything is abstract, in fact, the table is used to store data.

2, the composition of the table

DESC Dept

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DEPTNO: The column type is number (2), which means that the value of the column allows only a maximum of two characters (an English character or a number of one character, and a Chinese character occupies two characters), the number can be 1 or 99, but not 100 (this is 3 characters); Null indicates that the inserted data cannot be empty.

Dname: The column type is VARCHAR2 (14), which indicates that the column allows a maximum of 14 characters. That is, the department name cannot exceed 14 English letters or 7 Chinese characters, and this column does not have NULL, that is, no value can be entered.

LOC: The column type is VARCHAR2 (13), which indicates that the column allows a maximum of 13 characters. Is that the location name cannot exceed 13 English letters or 6 characters, and this column does not have NULL, that is, no value can be entered.

3. The underlying column has those constraints

Number: The Arabic numerals are represented

The text represents a string

How to create a table and what to look for in a design table