Syntax differences between MySQL and Oracle

MySQL and Oracle Grammatical differences

One 、 Data type differences

Category	Oracle	MySQL	difference
date	Date	Date、Time、Datetime	MySQL in Date It only means year, month and day ,Time It only means hours, minutes and seconds ,Datetime It means year, month, day, hour, minute, second Oracle in Date It means month, day, hour, minute, second and MySQL in Datetime equally
On the column	Sequence	AUTO_INCREMENT	MySQL Set the auto increment key on the table to realize auto increment ,Oracle It is to build a maximum value of the initial value of the sequence through the sequence
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Two 、 Database operation differences

Category	Oracle	MySql	difference
Parameter query	show parameter Parameters	show variables like ‘% Parameters %’
database	nothing	create database test_1;show databases;	MySQL You can create a database ,Oracle Just create instances , The user is in the instance , Or container database
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3、 ... and 、 Table operation difference

Category	Oracle	MySQL	difference
Create table	create table emp{ emp_no number(10) primary key, -- Primary key …}	create table emp01{emp_no int(10) primary key AUTO_INCREMENT,– The primary key increases automatically …}	MySQL No, number, But you can grow your reputation （AUTO_INCREMENT）,MySQL Yes double type .Oracle Self growth cannot be declared , Decimal only float type
Delete table	drop Table name	drop table if exists indicate	Oracle There is no exists keyword , If you want to achieve the same effect, you can judge whether there is one
Add columns	alter table emp add name varchar2(10);alter table emp add(name varchar2(10),password varchar2(30))	alter table emp add column name varchar(10);alter table emp add column name varchar(10),add column password varchar(30)	MySQL Adding fields requires add column+ The field name and type you want to add , If you want to add multiple fields, you need add column.Oracle Adding fields does not require column, When adding multiple fields, you only need to put them in the same bracket
Delete column	ditto , hold add Instead of drop	ditto , hold add Instead of drop	ditto , Replace the addition with deletion ,add Instead of drop
Change column names	alter table emp rename column name to username	alter table emp change column name username varchar(10)	MySQL adopt change column Original field Field to be changed The character type must be added .Oracle adopt rename column Original field to New fields Cannot have field type , Field type requires alter table Table name modify ( Field data type constraint condition )
Modify column type	alter table emp modify (name varchar2(30))	alter table emp modify column name varchar(30)	Oracle It cannot be modified when there is data listed, and it can be modified when there is no .MySQL It can be modified at any time , But when there is data, it may cause data loss , You can add temporary columns , After importing the data into the temporary column, delete the original column , And change the temporary column name to the original column name
Indexes	Creating an index makes little difference , When deleting an index, you can directly drop index indexName, Query index queries through views	To delete an index, you need to specify a table name ,drop index indexName on tableName,alter table tableName drop index indexName, direct show index from tableName You can find the index	MySQL Indexes can have duplicate names, so you need to specify the table name when deleting , So the index is table level ,Oracle The index in cannot have the same name , It is database level
An empty string	‘’ Namely null	'' and null There is a difference	Oracle in ’‘ and null There is no difference , But in MySQL in ’‘ Is for empty characters ,null There is nothing ’ vacuum ’, Try not to insert ’’
Partition table	It can realize automatic partition	No automatic partition	MySQL To realize automatic partitioning, you need to implement stored procedures

Four 、 Permission differences

Category	Oracle	MySQL	difference
Create user	stay create user You need to determine permissions when	direct create user user_name identified by user_password	Oracle Only two... Are needed connect,resource Permission to users , The user can operate the data , But it can't cross users .Mysql You need to give permissions separately in , You can also give it all , Different users can share some tables ,Oracle You need to add the identity of another user when accessing
Delete user	drop user user_name cascade	drop user user_name	cascade Delete all
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5、 ... and 、 Function difference

Category	Oracle	MySQL	difference
String function	insert(‘qwer’,‘asdf’,2)	insert(‘qwer’,‘asdf’)	Oracle You can specify the insertion position , from 2 Start inserting .MySQL Insert from the default location
	substr(‘asdf’,2,2)	substring(‘asdf’,2,2)	Only the function name is different , Other usages are the same
	length()	char_length()	Oracle in select length(‘asdf’) value from dual.MySQL in select char_length(‘asdf’) value
Control flow function	nvl(u.email_address,10)	ifnull(u.email_address,10) perhaps isnull(u.email_address)	Oracle If email It's empty 10 Replace ,MySQL If it is empty, it will not be replaced, but will be displayed as 10, If there is no number, it will be displayed as 1, If it is not empty, it will be displayed as 0
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unfinished .