Sort out MySQL common keywords
1. Demonstration of common keywords
user table structure ( id , name , age , sex ) – number , name , age , gender
| name | keywords | usage |
|---|---|---|
| Increase | insert | insert into user(name, age, sex) values(value 1, value 2, value 3); |
| delete | delete | delete from user where condition; |
| Revise | update | update user set field1=value1, field2=value2 where condition; |
| Inquire | select | select * from user; |
| deduplication | distinct | select distinct deduplicated fields from user; |
| Between | between | select * from user where age between 20 and 30; ( query for users between 20-30 ) |
| fuzzy matching | like | select * from user where name like 'zhang_%'; ( where _ matches one character and % matches one or more ) |
| Paging query | LIMIT | SELECT * FROM user LIMIT 5; ( query the first 5 record rows ) |
| Number of records | count | select COUNT (*) from user; ( query the number of all records in the user table ) |
| sum | sum | select sum (age) from user; ( query all age sums ) |
| max min | max 、 min | select max (age) from user; ( the maximum age is the same as the minimum ) |
| average value | avg | select avg (age) from user; ( average age of all people ) |
| sort | order by | select * from user order by age; ( default positive order from small to large, asc positive order, desc reverse order ) |
| grouping | group by | select sex,count(*) from user group by sex; ( group query for the total number of men and women ) |
| Filter after grouping | having | In fact, it is similar to the usage of where . After having, you can use the aggregate function where but not. After grouping and filtering, it is recommended to use the having keyword. |
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