MySQL Common syntax

1. Union merging of two or more SELECT statements
2.year (now ())-year (sbirthday) Get current Age

3.order by sort default positive order desc reverse

4.group by grouping having a conditional judgment on group by data only

COUNT (*): Counts the number in a group, usually with "*" Parameters

Max (field name): Gets the maximum value in the Group for this field.

Min (field name): Gets the minimum value in the Group for this field.

sum (field name): Gets the sum of the fields in the group.

AVG (field name): Gets the average of the field in the group.

5. Like (Fuzzy Lookup): Grammatical form: xx as ' the character to look for '

% represents any number of arbitrary characters

_ represents any character of 1

6. Limit:
select * FROM table limit M,n
where m refers to the beginning of the record index, starting from 0, indicating the first record
n means starting from section m+1 and taking N.
SELECT * FROM tablename limit 2,4
Take out 3rd to 6th, 4 records

7. The difference between or and and

Or:or is ' or ' meaning, as long as one of the conditions is established.

And:and is ' with ' meaning, juxtaposition, two conditions to be set up

MySQL Common syntax