MySQL basic queries and operators

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Catalog

MySQL The basic query

Query concept ：

1. Check all products ：

2. Query a column ：

3. Alias query ：

4. Column alias query ：

5. To duplicate value query ：

6. The query result is an expression -- Arithmetic query

Operator

1. Raise the price of all commodities 10%:

2. Query the trade name as “ Haier washing machine ” Information about our products

4.like----- Wildcard match

（1） Query contains ’ pants ‘ All commodities of the word ：

（2） Query to ’ The sea ‘ All goods that begin with the word ：

（3） The second word is ’ Kou ‘ All of our products ：

5.NULL Use ：

6. Use of functions ：

（1）least For the minimum ：

（2）greatest For maximum

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MySQL The basic query

Query concept ：

Query is an important function in database management system , Data query should not simply return the information stored in the database

You should also filter the data as needed and determine what form the data is displayed

1. Check all products ：

select   * from Table name ;

2. Query a column ：

select Name 1, Name 2 from Table name ;

3. Alias query ：

select * from Table name as Alias ;

4. Column alias query ：

select Name 1 as Alias , Name 2 as Alias ,from Table name ;

5. To duplicate value query ：

When all columns are the same, the duplicate value will be removed （ In general, it will not appear --- Primary key ）

select distinct Name from Table name ;

6. The query result is an expression -- Arithmetic query

select Name , Name +10 Alias from Table name ;

Alias used     The result is +10 Show alias after       The original table data will not be modified ;

Operator

Operator concept ： After the table structure in the database is determined , The meaning of the data in the table has been determined , adopt mysql Operator can obtain another kind of data other than the table structure .

The following illustrates the application of operators with examples

1. Raise the price of all commodities 10%:

select pname ,price*1.1 as new_price from Table name ;

2. Query the trade name as “ Haier washing machine ” Information about our products

select *from Table name where pname=' Haier washing machine ';
（1）select *from Table name where price between   100 and 200;

  (2) select *from Table name where price >=100 and price<=200;

3. The inquiry price is 200 or 800 All products of ：
select *from Table name where price in（200,800）;

in If only one value in the keyword bracket is satisfied

4.like----- Wildcard match

（1） Query contains ’ pants ‘ All commodities of the word ：

select * from Table name where pname like ’% pants %‘;

（2） Query to ’ The sea ‘ All goods that begin with the word ：

select * from Table name where pname like ’ The sea %‘;

（3） The second word is ’ Kou ‘ All of our products ：

select * from Table name where pname like ’- Kou %‘;

5.NULL Use ：

NULL Out-of-service =    because NULL Not equal to any value （ Including itself ）

Inquire about id Not for NULL  The goods

select * from Table name where Name is not NULL; 

6. Use of functions ：

（1）least For the minimum ：

select least（5,10,20）;

select least（5,10,20）as smallnumber;

select least（5,null20）;

If there is NULL    Will not be compared   Direct output NULL 

（2）greatest For maximum

select greatest （10,30,20）as bignumber;

select greatest （10,null,20）as bignumber;

If there is NULL    Will not be compared   Direct output NULL