MySQL basics --- data query 01

1. Query all information
   select * from table name;
2. Query the corresponding column
   select column name to be viewed 1, column name to be viewed 2 ... from table name;
3. Take alias
   select column name to view 1 [as] alias, column name to view 2 [as] alias… from table name;
4. Filter duplicate data
   select distinct column name from table name; (column name is the name of the filtered column)
5. The selection
   column is an expression: Select column name (number type column) * 0.8 from table name;
   Ceil (value): round up example: ceil (321.1) = 322
   Floor (value): round down example: floor ( 321.9) = 321
   Round (value): round to five rounds Example: Round (321.1) = 321 Round (321.9) = 322
6. Query condition
   Select * from table name where condition
7. Relational operator

<> = <=! = (<>) Is not equal to =

8. Logical operator
   And (both)
   Or (or)
   Not (negated)
   isNull (is empty)