MySQL must know and know!!! Reading this article is enough!!!

Catalog

SELECT sentence

keyword

Sort

Single column sort

Sort by multiple columns

Specify sorting direction

Sort + Limit

WHERE keyword

AND  OR key word

IN The operator

NOT The operator

wildcard

LIKE wildcard

% wildcard

Underline “_” wildcard

Search with regular expressions

REGEXP

  Conduct OR matching

Match one of several characters

“-” character

“\\” Match special character

  Match character class

Create calculated fields

Splices join values together to form a single value

  It's called AS Key words are given to

Perform arithmetic calculations

MySQL function

  Text processing function

Upper（） The function converts text to uppercase

Common text processing functions

Date and time processing functions

Commonly used date and time processing functions

  Numerical processing function

Summary data

Concept

Aggregation function

DINTINCT Parameters

The data packet

GROUP　BY Clause

  Filter grouping

inductive SELECT Order of clauses

  Subquery

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SELECT sentence

keyword

SELECT * FROM  products                "*"  wildcard

SELECT  DISTINCT   id  FROM  products         DISTINCT Weight removal

SELECT   name  FROM  products   LIMIT   5                 LIMIT instructions MySQL Return no more than five lines

LIMIT3,4     Refers to the subordinate line 3 At the beginning 4 That's ok

Sort

Single column sort

SELECT  name  FROM   products  ORDER   BY name

take name Columns are sorted alphabetically

Sort by multiple columns

SELECT  id, name, price  FROM  products  ORDER  BY   price ,name

First by price, then by name

Specify sorting direction

SELECT   id,price,name  FROM  products  ORDER   BY  price  DESC

DESC  null （ Specify only the column names that precede ）

If you want to sort in descending order on multiple columns , You need to specify... For each column DESC keyword

Sort + Limit

SELECT  price   FROM products  ORDER  BY  price  DESC  LIMIT   1

WHERE keyword

SELECT  name,price  FROM  products  WHERE  price = 2.50

ORDER  BY  Should be located WHERE after

WHERE Clause operator <,>,=,>=,<=,!=,<>,BETWEEN

WHERE price  BETWEEN  5  AND  10

WHERE  price   IS   NULL

* Cannot return with NULL Row of values

AND  OR key word

WHERE  id=1003  AND   price<=10

AND Join keywords

OR Or key words

use Parentheses clearly Group

IN The operator

 IN And OR The function of has the same function , however IN It's better

NOT The operator

NOT  WHERE Keyword used in clause to negate a condition followed by a condition

SELECT  name,price  FROM  products WHERE  id  NOT  IN（1002,1003）

It means match 1002 and 1003 In addition to the id

wildcard

LIKE wildcard

% wildcard

% Means any character appears any number of times

for example , Find all the words jet The first product , You can use the following statement

SELECT  id,name  FROM  products  WHERE  name   LIKE  ‘jet%’;

Empathy ‘%anvil’ Can match any location containing text anvil Value

‘s%e’ Can match to s Start with e All values at the end

% Wildcards cannot match NULL

Be careful MYSQL Search can be case sensitive , It depends on your MySQL Configuration of

Underline “_” wildcard

Underline and % The usage is the same , But underscores can only match a single character, not multiple characters .

Take a chestnut

SELECT  id,name  FROM  products  WHERE  name  LIKE  ‘_  ton  anvil’;

Search with regular expressions

REGEXP

SELECT   name  FROM  products  WHERE   name  REGEXP  ‘1000’  ORDER  BY  name;

MySQL Regular expressions for are not case sensitive , To be case sensitive , Can be used BINARY keyword , for example

"." Can match any character

WHERE   name  REGEXP  BINARY  ‘JetPack  .000’

  Conduct OR matching

WHERE  name  REGEXP  ‘1000|2000’  ORDER  BY name

Match one of several characters

SELECT  name  FROM  products  WHERE  name  REGEXP  ‘[123] Ton’  ORDER  BY  name

Regular expressions are used here [123] Ton, It means match 1 or 2 or 3, Function like IN keyword , yes [1|2|3] Abbreviation

Character sets can also be negated , Place a... At the beginning of the collection "∧" that will do , for example [∧123], You can match the division 123 Other characters

“-” character

“-” It can be used to define a range , for example [1-9],[a-z] Fine

Take a chestnut

SELECT   name  FROM  products  WHERE  name  REGEXP ‘[1-5]Ton’

“\\” Match special character

To match these keyword characters , for example “-”,“.” How should we do this

To match special characters , It must be used. “\\” As the leader , for example

SELECT  name  FROM  products  WHERE  name  REGEXP  ‘\\.’

“\\” Also used to refer to metacharacters

To match the backslash “\” Character itself , Need to use "\\\"

  Match character class

  The regular expression section is omitted

Create calculated fields

When we need to retrieve the transformation from the database , Calculation , Or formatted data , Calculation fields are needed

Splices join values together to form a single value

The solution is to splice the two columns , You can use Concat（） Function to splice two columns

  It's called AS Key words are given to

SELECT　Concat（RTrim（name,'  (',RTrim(country),  ')') AS  title  FROM  vendors  ORDER  BY  name ;

The sentence itself is the same as the previous sentence , But it indicates SQL Create a calculation named title Calculation field of , Any client can reference this column by name

RTrim You can remove all the blanks on the right ,LTrim You can remove all the blanks on the left ,Trim You can remove the spaces on both sides

Perform arithmetic calculations

 

MySQL function

  Text processing function

Upper（） The function converts text to uppercase

SELECT  name,Upper（name）  AS  name——upcase

FROM  vendors

ORDER  BY  name

Common text processing functions

Date and time processing functions

Commonly used date and time processing functions

 MySQL Date format used , Date format must be yyyy-mm-dd.

for example

SELECT  id  ,num  FROM  orders  WHERE  date=‘2005-09-01’;

To retrieve all the data in September , You can use ：

SELECT  id,num  FROM  orders  WHERE  Date（order_date)  BETWEEN '2005-09-01' AND '2005-09-30';

or

  Numerical processing function

Summary data

Concept

We often need to aggregate data without actually retrieving them , At this time, we need to use the aggregation function

  Examples of this type of retrieval are ：

*  Determine the functions in the table

*  Get the sum of row groups in the table

*  Find the maximum, minimum and average values in the table

Aggregation function

Take the first function AVG（） For example

SELECT  AVG(price) AS avg_price  FROM  products;

The return value is avg_price, by products The average price of all products in the table

 

 

DINTINCT Parameters

DINTINCT Weight removal can be achieved , The same number is not included in the calculation range of the aggregate function

The data packet

GROUP　BY Clause

Take a chestnut

 

GROUP　BY It can be grouped according to the specified data , Then aggregate the data in each group

  Filter grouping

We know WHERE It has the function of filtration , however WHERE Is to filter rows ,  For grouping , We can use HAVING Clause to filter the grouping , Syntax and WHERE identical .

for example

WHERE And HAVING At the same time

inductive SELECT Order of clauses

  Subquery

That is, queries nested in other queries

—— To be continued ——

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