Some basic sql statements, recently looked at sql statements, and sql optimization, just made some summaries in the notes, not comprehensive, and I will add some in the future.
Sql basic content:
1, select * from user query user table all
2. Select distinct user_age, user_name from user to query all the unique user_age, user_name.
3. Where to do conditional query:
Some common operators:
= Equal; <> not equal; <= less than or equal;> = greater than or equal to;
between and; like fuzzy query; in specifies multiple possibilities for a certain column.
4, the use priority of and and or: () not and or
SELECT * FROM Websites WHERE alexa > 15 AND (country='CN' OR country='USA');
5. The order by keyword is used to sort the result set. Ascending ASC (default) Descending DESC
SELECT column_name,column_name FROM table_name
ORDER BY column_name,column_name ASC|DESC;
6, insert into insert data into the database
insert into 表名 values （value1,value2,value3,...）;
insert into 表名 （column1，column2...）values (value1,value2...）;
7, update update the database
update table name set column1 = value1, column2 = value2 ... where condition.
UPDATE Websites SET alexa='5000', country='USA' WHERE name='111';
8, create database database name
9, delect from table name where condition deletes a record of a table.
