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not divided. Each column is an indivisible basic data item. 2) Example: Suppose we have a student table, the fields include: Id,name,age,contact, as follows: When we need to query the students according to QQ, we can not find out, so the above design is not in line with 1NF. We can split the contact field into phone and QQ, as follows: This will satisfy the 1NF. 2. Second Paradigm　 1) Concept: Based on the 1NF, the non-primary attribute is completely dependent on the primary key. 2) Example:

database, the first paradigm (1NF) is the basic requirement for relational schemas, and a database that does not meet the first normal form (1NF) is not a relational database. second Normal form (2NF): The non-keyword in the data table does not have a partial function dependency on the candidate keyword (some of the function dependencies refer to the case where some of the fields in the composite keyword determine a non-critical field), then the second normal (completely dependent on the pri

keywords.Assume that the selection relationship table is Selectcourse (school number, name, age, course name, score, credits), keyword for the combination of keywords (study number, course name), because of the following decision relationship:(School number, course name) → (name, age, score, credits)This database table does not meet the second normal form because of the following decision relationship:(cou

Label:1. First paradigm (1NF) The emphasis is on the atomicity of the column, that is, the column cannot be divided into several other columns.Consider a table that says "Contacts" (name, gender, phone)If a contact has a home phone and a company phone in a real-world scenario, the table structure is not designed to reach 1NF. To comply with 1NF we simply split the column (phone), namely: "Contact" (name, gender, home phone, company phone). 1NF is good to distinguish, but 2NF and 3NF are easy to

-called complete dependency refers to the inability to exist only to rely on the main key part of the property (with function dependent w→a, if there is XW, there is x→a established, then called W→a is a local dependency, otherwise it is called w→a is a complete function dependency). If present, then this part of the attribute and primary key should be separated to form a new entity, and the new entity is a one-to-many relationship with the original entity. Assume that the selection relationshi

each employee can be uniquely differentiated. In short, the second normal form (2NF) is completely dependent on the primary key for the non-master attribute. The so-called complete dependency refers to the inability to exist only to rely on the main key part of the property (with function dependent w→a, if there is XW, there is x→a established, then called W→a is a local dependency, otherwise it is called w→a is a complete function dependency). If present, then this part of the attribute and p

candidate keywords.Assume that the selection relationship table is Selectcourse (school number, name, age, course name, score, credits), keyword for the combination of keywords (study number, course name), because of the following decision relationship:(School number, course name) → (name, age, score, credits)This database table does not meet the second normal form because of the following decision relatio

columns. Therefore, it is impossible for you to design a database that does not conform to the first paradigm in your existing DBMS. The second paradigm (2NF ): A partial function dependency of a non-critical field on any of the candidate key fields is not present in the database table (some of the function dependencies refer to situations where some fields in the composite keyword determine non-critical fields), or all non-critical fields are completely dependent on any set of candidate keywo

specified table in the FROM clause. For example, if the "name" field is not added when the CS_XS view is defined, an error occurs during data insertion. Www.2cto.com 8. Modify the data using the UPDATE statement. You can modify the data examples of the basic table through the view: increase the total credits of all students in the CS_XS view by 8. UPDATECS_XS SET total credits = total

I am going to prepare for a review recently. Taking the MSSERVER2005 examination is a summary of the relevant SQL statements. Generally, I have not written any frequently-used SQL statements, which may be used and are not frequently used, however, it is not unnecessary syntax, and we hope to use the SQL statement SELECTDISINCT (student ID) for everyone. The level of CASEWHEN total credits 50THEN pass WHEN total cr