This article reproduced from:http://www.cnblogs.com/longyi1234/archive/2010/03/24/1693738.html Blue Sky First, what is the primary key, foreign key relational database in a record in a number of attributes, ifAn attribute group (note is a group) can
A common index of a database is typically a single field, and if multiple fields are combined, a composite index is formed. For a composite index, ifWhat happens when you make a conditional query on one of the fields?First, examplesMysql>Show CREATE
How to convert the key index of an array into a digital index?
For example, the information I read from the INI file is a one-dimensional array:
This is my INI file
[web]
host = localhost
Connuser = root
Connpwd = root
CONNDB = Myoffice
PHP
The first step in a content-grabbing eye is a headline, but the real test is: How do you keep their attention after attracting the audience? Yes, the importance of the title is undeniable, but the reader can not go to read, the click-through rate is
1, the creation of the primary keyMethod One: Declare the field PRIMARY KEY constraint directly in the SQL statementCREATE TABLE table_name (ID type[length] constraint pk_name primary key,name tyoe[length],age type[length],class_id);Method two:
Concept:A primary key (primary key) uniquely identifies a property or group of properties for a row in a table. A table can have only one primary key, but there may be multiple candidate indexes. Primary keys often form referential integrity
We know that Oracle automatically indexes the primary key columns of the table, and this default index is the normal B-tree index. The default B-tree index is not ideal for situations in which primary key values are added sequentially (incremental
The role of the primary and foreign keys of sql:Foreign key value rule: A null value or a reference primary key value.(1) When a non-null value is inserted, it cannot be inserted if the value is not in the primary key table.(2) When updating, you
Transferred from: http://blog.csdn.net/duck_arrow/article/details/8264686Concept:A primary key (primary key) uniquely identifies a property or group of properties for a row in a table. A table can have only one primary key, but there may be multiple
Seems to have the same effect, adding a key to the table and set up the index of the table, can be fast data query. The difference between them is that they are on different levels.Key is a part of the relational model theory, such as a primary key (
First, what is the primary key, foreign key:There are several attributes in a record in a relational database, which can be a primary key if one of the attribute groups (note is a group) uniquely identifies a record:Student Table (School number,
Case descriptionDuring a timed script run, it is found that when the SQL statement of the backup table runs concurrently with the SQL statement that deletes the data in the table, MySQL detects the deadlock and prints out the log.Two SQL statements
found that when the SQL statement of the backup table runs at the same time as the SQL statement that deletes part of the data from the table, MySQL detects the deadlock and prints out the logCase descriptionDuring a timed script run, MySQL detects
Case descriptionDuring a timed script run, MySQL detects a deadlock and prints out a log when the SQL statement that backs up the table runs concurrently with the SQL statement that deletes the data from the table.The two SQL statements are as
Case DescriptionDuring the running of the scheduled script, it is found that when the SQL statement for backing up the table and the SQL statement for deleting some data in the table run simultaneously, mysql will detect the deadlock and print the
Today is. I was planning to mix the direction key index and other indexes into other index logs, but I still feel that this part is too important. Record the arrow key index notes here. What is a direction key index? The direction key index is also
Case DescriptionDuring the running of the scheduled script, it is found that when the SQL statement for backing up the table and the SQL statement for deleting some data in the table run simultaneously, mysql will detect the deadlock and print the
This is a user table associated with the Group table uid,group_id is the only pair.
"Scenario 1: (unique) composite Index"UNIQUE KEY uid_group_id (uid,group_id)
"Scenario 2: Composite primary Key"PRIMARY KEY (uid,group_id)
1: I hope the great
Original address: http://blog.itpub.net/29254281/viewspace-1398273/ MySQL chooses what to think before you can read the isolation level repeatedly. Gap Lock MySQL before use There are three must be aware of: (with the depth of understanding
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