Tags: auto-generate app Query index primary KEY COM nbsp FOREIGN KEY constraint constraintNon-null constraint: When the column is set, the default can be empty, the setting data cannot be empty after removing the checkmark;Unique constraint: Set in key, UNIQUE constraint name, type unique, column name; After the applic
Oracle Table-Building, primary key, foreign key basic syntax
-Create TABLE syntax:CREATE TABLE Table name (Field name 1 field type (length) is empty,Field Name 2 field type is NULL);
-Add primary keyALTER TABLE name add constraint primary
In other words, I have a forum with two tables, one with the primary thread and the other with the reply. The primary key is the only field in the table that recognizes records, it is generally the post ID, which is reflected in the access time, for example, thread. PHP? Id = 1 indicates that I want to access a post whose ID is 1 ~ Let's talk about the foreign
illustrate how to use inner joins and nested queries to implement multi-table queries. In fact, all databases are the same, and SQL statements are generic.I. BASIC OBJECTIVESIt is known that in the test database, the school database can be self-contained, the following table exists:(1) The student table I_student, which records the data of all the students in the school, indicates that there are 3 students in the school a,b,c(2) Class table I_class, which records all classes in the school data,
Several concepts need to be clarified:
1) Candidate Key: the value of an attribute group in a link uniquely identifies a tuples. If any attribute is removed from this attribute group, it does not have this property, such an attribute group is called a candidate code.
2) primary key: when multiple candidate codes exist, you can select one as the
Tags: c style http a width comAssociation mappings: one-to-oneOne to one relationship is the relationship between the team and the team's address, a team only has an address, and an address area has only one team.There are two kinds of data table-to-one relationships: a foreign key association and a primary key association. This is illustrated below:One-to-one fo
1, right-click on the root directory under the connection to create the databaseEnter the database name, set it up, and click on the page to determine the success of the creation2. Double-click to open DatabaseThe first of these is the table, the most important and fundamental of the table.3, CREATE TABLE, find table Right-click, create table.First of all to determine the column, column name, the database do not use Chinese name to do the column name.Re-determine the value, type bit Boolean can
--Delete foreign keysSyntax: ALTER TABLE name DROP constraint foreign KEY constraint nameSuch as:ALTER TABLE STU_PKFK_SC DROP constraint fk_sALTER TABLE STU_PKFK_SC DROP constraint Fk_c--Add foreign keysSyntax: ALTER TABLE name ADD constraint foreign KEY constraint name foreign key (column name) references Reference foreign k
We are after the insert operation of the record of the table. Having such a requirement would require the primary key ID of that record to be insert. And the primary key ID of the table is the primary key self increment.It is not
Tags: on as SQL type Oracle table text class ROMQuery all columns and their properties for a table:Select From User_tab_columns t,user_col_comments Cwhere t.table_name = c.table_name and T.column_name = c.column_name and t.table_name = women;To find the primary key for a table:Find the foreign key of the table (including the name, the table name of the referen
SQL statement used to query the foreign key information of a table's primary key. In my BSOOC, I need an SQL statement to query the foreign key information of the table's primary key. Last night I studied it at AM and finally achi
Some SQL (under Oracle) summaries used in the project: 1. Find all indexes of the table (including index name, type, constituent column) 1 Select T.*,i.index_type from User_ind_columns t,user_indexes i where t.index_name = I.index_name and T.tab Le_name = i.table_name and t.table_name = table to query2. lookup table's primary key (including name, constituent column) 1 Select cu.* from User_cons_columns cu
GO--determine if the table exists in the way 1if object_id(N'Ef_user'N'U') is NULL--determine if the table exists in the way 2--If not EXISTS (SELECT * FROM dbo. SysObjects WHERE id = object_id (N ' [Ef_user] ') and OBJECTPROPERTY (ID, ' istable ') = 1)begin--directly create a table with the self-increment and specify a PRIMARY KEY constraintCREATE TABLE [dbo].[Ef_user]( [ID] [int] Identity(1,1) not NULL
When you delete some of the tables, you will often encounter a primary key that is referenced by a foreign key in some relational tables and cannot be deleted, and this is the time to find out which table the primary key is referenced, and there is a view in Oracle that can
ORACLE: primary key, foreign key, Uniqueness constraint, and index of the query (View) Table
1To search for all indexes of a table (including index names, types, and columns ):Select T. *, I. index_type from user_ind_columns T, user_indexes I where T. index_name = I. index_name and T. table_name = I. table_name and T. table_name =Table Name
2, Query the table
It means you have duplicate records in your data.Two cases1. Existing tables and duplicates to import dataThis can be done by establishing an association between two tables, and the primary key cascade to find duplicate records2. Duplicate records exist in the table to be importedDuplicate records in a table can be identified by a statement similar to the followingSelect Studentcode from Studentscore GROUP
Select B. table_name primary key table name, B. column_name primary key column name, A. table_name foreign key table name, A. column_name foreign key column name From ( Select A. constraint_name, B. table_name, B. column_name,
Because the data structure design of some modules of the project is not strictly in accordance with certain specifications, the data structure can only be queried from the database. The information to be queried is as follows: field name, data type, whether it is null, default value, primary key, foreign key, and so on.
I searched for the above information on th
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