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auto-incrementing primary key. Before using PHP to insert data, I imported some data, similar to the following:
1 xx
2 ss
3 rr
Then insert it in PHP. After multiple inserts, it is as follows:
1 xx
2 ss
3 rr
4 ww
1 xx
2 ss
3 rr
5 ee
4 ww
1 xx
2 ss
3 rr
6 tt
5 ee
4 ww
However, after I only import the table structure, it is normal to use PHP to insert it. Howeve
the next, such as:
+ GG
+-II
How do you make it start from 0? (Or is it 1?) )
Really do not want to waste points, my problem is more, points or save a bit of it. If there is a satisfactory answer I will add points, if it can be fully resolved I will add 80 points, including the direct deletion of the phpMyAdmin database in the table records will not be a problem.
------Solution--------------------
Run SQL
. However, at the time of insertion, the id does not start from 0, but is a relatively large number. it should be the next of the last id used, as shown in the following code:
40 gg
41 ii
How can we make it start from 0? (Or 1 ?)
I really don't want to waste points. I have a lot of problems. I 'd like to save some points. If there is a satisfactory answer, I will add points. if it can be completely solved, I will add 80 points, including directly deleting the records in the
CodeAlter Table Add constraint Foreign Key References on Delete Restrict on Update Restrict;(constraint can be appended with the constraint name)The reason for the error is that the IDs of the previous two tables are of different types, one when int, and one when bigintWorkaround when modifying the table,Alter Table
can be fully resolved I will add 80 points, including the direct deletion of the phpMyAdmin database in the table records will not be a problem.
Reply to discussion (solution)
Run SQL:
ALTER TABLE ' Your table name ' Auto_increment=1
The precondition is that the current ta
1. Why composite primary key ing?In reality, we may encounter many tables that do not have a primary key. What kind of results will we use after ing them? Can we get what we want? The expected result is not obtained, and the following error may be returned:
Caused by: org. hibernate. AnnotationException: No identifier
Many people confuse primary key with a clustered index, or think it's the same thing. This concept is very wrong.
A primary key is a constraint (constraint) that is attached to an index that can be either a clustered index or a nonclustered index.
So having a primary
Question: Suppose there is a student score table (TB) as follows:Name Course ScoreZhang San language 74Zhang San Mathematics 83Zhang San Physics 93Zhang Sande language nullJohn Doe Language 74John Doe Mathematics 84John Doe Physics 94John Doe English 80Want to become (get the following result):Name Chinese mathematics Physics English German----------------Lee 474 84 94? 60Zhang 374 83 93 80?Here name and course determine only one record, as the
ainner join position pp on pp. lngpositionid =. flnginpositionidleft join employee e on e. lngemployeeid =. flngemployeeidwhere. flnginid
The preceding is a view in Oracle. This view is always not added several times.
The view is not added after vertices.
The reason is that in view SQL, the union all keyword EF cannot infer which is the primary key.
Solution:
1. Why do I have a composite primary key mappingIn reality we may encounter many tables that may not have a primary key, so what would be the result of using it after mapping? Is it normal to get what we want? The result should not get the desired result, and the resulting may be the following error:
caused by:org.h
Tags: Data rom primary key IDE entity insert Max Sele returnTable level, whose primary key is lid1.select Max (ID) from tableQuery statement: SELECT MAX (lid) from levelReturn Insert PRIMARY Key2.select last_insert_id (ID) from tableQuery statement: SELECT last_insert_id (li
Hibernate @ TableGenrator table management primary key generation policy, hibernate primary key generation@ TableGenerator: generates a table in the database to manage the primary
is not necessarily a primary key, but must be a unique index.
primary KEY constraints and uniqueness constraints are unique indexes.
FOREIGN KEY Constraint
SQL Server 2008Other versions
A foreign
.
In addition, when we need to replicate data between multiple databases (SQL Server's data distribution, subscription mechanism allows us to replicate data between libraries), auto-growing fields can cause primary key conflicts when data is merged. When you imagine that an order table in a database replicates a datab
(SQL The data distribution and subscription mechanism of the server allows us to replicate the data between libraries, and the autogrow field may cause a primary key conflict when the data is merged. Imagine that the order table in one database replicates the number of order tables in another library According to the
1. Create a new data table with the field ID, set the ID as the primary keyThe code is as follows: CREATE TABLE TB (ID int,constraint pkid primary key (ID))
performance of the sequence.
2. The syntax for removing the Oracle sequence is the drop SEQUENCE sequence name;
Using sequences creates cracks.The l sequence cracks in the following cases:• Rolling back• System Exceptions
Instance application:
1. Sqlplus Log In First:Sql> Conn Scott/tiger;2. Build table:drop table users;
CREATE TABLE users (
ID number
tables has been completed.2.2 Setting primary keys with SQL statements2.2.1 Select the database->sqltest, click New Query, notice in the upper left box is sqltest, not the words manually select.2.2.2 Enter the following code in the click New query interface:--This is the comment information in SQL, annotated with two minus signs.DropTable Student--Delete
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