[Learning Record] MySQL primary query statement (select,where)

The standard query statements are as follows

Select   Column name 1, column name 2, column name 3 from      table name

The statement returns all rows of the corresponding column in the table

If you want to retrieve all the columns in a table, you can use the *

Select *  from table name a

Because the table's non-code attributes allow duplication, it is found that there are duplicates in the search results, which can be filtered by distinct

Select distinct  from table name F

You can use the limit clause if you are only interested in the first few rows of the search results

select column name from   table name limit A, a,  b

This means that the output starts from line A with a total of B line elements, and if you do not provide a then start at line 1th

If you need to sort the results of a search, you can use the ORDER BY clause

Select column name A, column name B from    table name  order by column name B; Select column name A, column name B from    table name  orderby  desc;

That is, sorting according to column name B, plus desc for the reverse order, you can also follow the column name by commas separated by a second row sequence. For example, order by column name B desc, column name C

Data filtering via where

Select  Column name from    table name  where   name='a'

Note that if you need to sort the results, the where must precede the order by

Where-supported conditional actions

For example, the Select product from the products where the price between 5 and 10

Where also supports the determination of NULL values

Select product from products where attr is null

About where more advanced usage

where supports and and or operations between multiple conditions, but note that the and priority is higher than or, and if necessary, parentheses

The where also supports in and not

Select  Student from    stus  where   in (+) Select  Student from    stus  wherenot in     (18 ,)

It is worth noting that the first statement here matches age=18 or 20, and the second match is that age is neither equal to 18 nor equal to 20.

Instead of 18 to 20.

[Learning Record] MySQL primary query statement (select,where)