15-07-16 Database--Delete and change

The string is enclosed in single quotation marks

The comparison in the database is =, not the double equals sign

Logic and

Logical OR OR

Logical non-not

CRUD Operations

I. C:create added, created, adds data to the database.

Insert into table name values (' K009 ', ' Apple ', 3.0, ' gaoqing ', 90, ')--add data to parentheses

Insert into table name (ids,name,price,source,numbers, column name) VALUES (' K010 ', ' Apple ', 3.0, ' gaoqing ', 90, data)

Two. R:retrieve search, query, query data from the database.

A row in a database table is called a record, and a column is called a field.

The query does not modify the actual table data for display purposes only.

Three. U:update modify the data from the database table.

Update table name set column name = ' data ' where row name = ' which line '

Four. D:delete Delete, delete data from the database.

Delete from table name where column name = ' Data '

Transaction: An error has occurred and can be rolled back

Add transaction: Begin Tarn--Add restore point

Rollback: rollback--restore

--Query

1. Query all select * FROM table names

2. Check the specified column select column name 1, column name 2 from table name--Chado column separated by commas

3. Replace column name Select column name ' Replace name ' from table name--replace multiple column names separated by commas

4. Check the specified line select * from table name where column name = ' Data '--* denotes all

5. Check the specified row by condition check select * FROM table name where column name = ' data ' and column name = ' Data '

6. Check the specified row by range select * from table name where column name between 2.0 and 4.0--2.0 to 4.0 data

7. Check the specified line, discrete check select * FROM table name where column name in (90,80,70)--Check the column that appears 90.80.70

8. Go to re-query select DISTINCT column name from table name--Remove duplicate query

9. Fuzzy Query select * FROM table name where column name like '% account '-check end of account

SELECT * FROM table name where column name like ' Account% '-Check with account opening

SELECT * FROM table name where column name like '% account% '-check to include account

SELECT * FROM table name where column name like '% account _ '-check account after only one character

10. Sort By Column name select * FROM table name ORDER BY column ASC-row ascending By column name, if not ASC by default in ascending order

SELECT * FROM table name ORDER BY listing desc-Sort By column name in descending order

SELECT * FROM table name order BY column name 1, column name 2--first column name followed by the last column name row

11. Return Data Select COUNT (*) from table name--Returns how many data are in the table

Average select AVG (column name) from table name--Returns the average of a column

Sum select SUM (column name) from table name--Returns all data for a column and

Max select max (column name) from table name--Returns the maximum value in a column

Min. Select min (column name) from table name--Returns the minimum value in a column

12. Add a new column of SELECT *, (column name *0.8) as ' discounted price ' from table name-add a column that is not in the database, here is the price column after adding 80 percent

13. Group Select column names by column name, COUNT (*) from table name Group BY column name

Filter Select column name after grouping, COUNT (*) from table name Group BY column name having COUNT (*) >1--data that is greater than 1 is returned according to a column group

15-07-16 Database--Delete and change