Single-table query:
Basic query:
select the column name
from table
where conditions
group by column name
order by column name
The second condition having // query, often used in conjunction with the group by using
The number limit
where clause comparison operators:
= ！= >= <=
like not like
is null
between...and...
in (value 1, value 2)
group by:
Different values of column groups, often with avg, sum function together with other polymeric
order by:
Sort in ascending order by default. desc asc Ascending Descending
Tsuhaifu:
- % Of one or more characters
- _ Single character
If desired query packet containing 10-15% or _ (i.e.% and _ the wildcard), the use of Escape, for example:
select * from tb1 where addr like '% /% g%' escape '/' Finds% g of (the escape / may be replaced by other characters)
select * from tb1 where addr like '% a% g%' escape 'a' (a% after the wildcard)
where和having：
- where it can not be used in conjunction with aggregate functions, such as:
where sum (cnt)> 3 errors
having sum (cnt)> 3 correct
- where views and tables acting, having the role of the group
- where before the packets and aggregation, select input line (which controls operation which aggregates into the row); HAVING packet and after aggregation, the packet selection row
- having generally follows the group by, the implementation of part of the working group of records selected, where it is to perform all data to work
distinct：
Query the selected column, different values of the line
select distinct column 1, column 2 // distinct from table on the back of the column 1, column 2 are valid
select column 1, row 2, column 3 from table group by row 1, column 2, column 3
In most cases, a DISTINCT clause can be considered as a special case of GROUP BY For example, the following two queries are equivalent:. (Distinct group by clause is a special case, the following two statements equivalent)
select distinct c1, c2, c3 from t1 select c1, c2, c3 from t1 group by c1, c2, c3
Subquery:
Multi-table query:
En
Left connection
The right connection
Outer join