1、By default, Mysql compares strings in a case-insensitive manner, and if you want to make case-insensitive comparisons, you can add the Binary keyword, which means that strings are handled binarily. When comparing operations on strings, MySql will distinguish the size of strings.Write.
For example:
2、When a number and a string are operated on, the string is converted to a number according to certain rules. If the first bit of the string and several consecutive digits after it are numbers, it is converted to the value of the number, otherwise, it is converted to 0.
For example:
select * *Representing all
Query multiple fields
select Field 1, field 2, field 3
Polymerization function count(*)
Statistics
select count(*)
sum()
Summing up
select sum() Or select sum (CJ)
avg()
average value
select avg() Or select AVG (CJ)
max()
Maximum value
select max() Or select max (CJ)
min()
minimum value
select min() Or select min (CJ), min (CJ).
Examples:
#For the 001 students, the highest score, the lowest score, the total sc...
1. Equivalent connection
Principle: form a large logical table with multiple single tables.
Grammar:
select * from Table A, table B where table A. primary key = table B. foreign key and query condition
select * from Table A, table B where Table A. primary key = table B. foreign key and C. primary key =B. foreign key and query condition
Two. Internal connection
First judge, then connect.
The result of internal connection is the same as the result of equivalent connection.
Syntax: two tables
select *
from Table A inner join table B
on Table A. primary key = table B. primary key
whe...
OracleUser creation and permission settings
Jurisdiction:
create session Allow users to login to database privileges
create table Allows users to create table permissions
unlimited tablespace Allows users to build tables in other table spaces.
Role:
connect
resource
dba
CONNECTRole: –It is a typical right to end-users, the most basic power.Ability to connect to the ORACLE database and do SELECT, UPDATE, INSERTT, etc. when you have access to other users’tables. ALTER SESSION –Modify the session ...
select * from tblConcludingApplication where States <> 2 and tblInternShipsId=” + sid + ”
MySQLYou can open MySQL’s information_schema database if each table in the database takes up space and the number of rows it records. There is a TABLES table in the library. The main fields of the table are:
TABLE_SCHEMA : Database nameTABLE_NAME: table nameENGINE: storage engine usedTABLES_ROWS: record numberDATA_LENGTH: data sizeINDEX_LENGTH: index size
The size of the space occupied by a table is equivalent to the size of the data and the size of the index.Examples:
1、View all the table sizes of the enrolment_db Library:
select table_name,table_rows from tables where TABLE_SCHEMA =...
On August 28, local time, Oracle officially announced the release of Oracle Solaris 11.4 GA stable version, nearly three years after the release of the previous version 11.3. Oracle product management director Scott LynnThis is the best version of the four Oracle Solaris versions he has participated in.
The news about Solaris is also a little surprising to you. According to our previous reports, Oracle has erased Solaris 12 from the roadmap and fired all Solaris technicians, although there was no official announcement.B, but you can assume that Oracle Solaris 12 has actually been ...
> = On the left, run to see = right.
3，Static functions.
Compile time: refer to whether there are invocation members in the class of the referenced variable.
Runtime: it also refers to the members who are invoked in the class that the reference variable belongs to.
Why is this so?Because static methods do not belong to the object, but belong to the class that the method belongs to.
Invoking the static method reference is the static method in which class the reference is invoked.
