Có 100+ tài liệu thuộc chủ đề "database SQL"
tailieu.vn Xem trực tuyến Tải xuống
CREATE TABLE AssignmentSchedule (ssn CHAR(9) NOT NULL. CREATE TABLE PilotSkills (pilot CHAR(15) NOT NULL, plane CHAR(15) NOT NULL, PRIMARY KEY (pilot, plane));. CREATE TABLE Hangar. This not the sort of thing that newbie SQL programmers can pull out of their hats, but they can write “SELECT pilot FROM QualifiedPilots;”. CREATE TABLE Stores. (store_nbr INTEGER NOT NULL PRIMARY KEY, store_name CHAR(35)...
tailieu.vn Xem trực tuyến Tải xuống
Is very like a spear!”. “I see,” quoth he, “the Elephant Is very like a snake!”. “I see,” quoth he, “the Elephant Is very like a rope!”. 7.1 VIEW Naming Conventions Are the Same as Tables 135. 7.1 VIEW Naming Conventions Are the Same as Tables. It consists of rows and columns, exactly the same as a base table. A...
tailieu.vn Xem trực tuyến Tải xuống
He was attempting to construct an entire report in the database by using UNIONs to get the 12 lines of the report in the right order, by assigning them a letter of the alphabet. The whole thing would take several pages to show, but it is an extraction of the printout lines that were constructed from just the General Ledger....
tailieu.vn Xem trực tuyến Tải xuống
Every SQL product has some kind of 4GL language that allows you to write stored procedures that reside in the database and that can be invoked from a host program. The users can only do what the stored procedure allows them to do, whereas dynamic SQL or other ad hoc access to the database allows them to do anything to...
tailieu.vn Xem trực tuyến Tải xuống
6.2.4.3 Use CASE Expressions, Not Complex Nested Predicates An advanced trick in the WHERE clause is to use a CASE expression for a complex predicate with material implications. If you forgot your freshman logic, a material implication logical operator is written as an arrow with two tails, and it means “p implies q” or “if p is true then q...
tailieu.vn Xem trực tuyến Tải xuống
CASE WHEN <value exp #1>. IS NOT NULL THEN <value exp #1>. ELSE <value exp #2>. COALESCE (<value exp #1>, <value exp #2>. ELSE COALESCE (<value exp #2>. <value exp #2>. ELSE <value exp #1>. SELECT a, b, c FROM Foobar WHERE a = b AND b = c AND c = a;. SELECT a, b, c FROM Foobar. SELECT...
tailieu.vn Xem trực tuyến Tải xuống
SELECT O1.order_nbr,. WHERE O1.order_nbr = D1.order_nbr AND D1.dept = 'mens wear';. ON O1.order_nbr = D1.order_nbr AND D1.dept = 'mens wear';. ON O1.order_nbr = D1.order_nbr WHERE D1.dept = 'mens wear';. loan_amt AND monthly_expenses <. 0.25 * loan_amt OR collateral >. 2.00 * loan_amt AND age >. loan_amt AND age >. 2.00 * loan_amt AND Age >. 0.50 * loan_amt;. loan_amt. 0.25...
tailieu.vn Xem trực tuyến Tải xuống
We build the CROSS JOIN of the two tables. Scan each row in the result set.. You also remove all rows derived from it from the CROSS JOIN.. Table1 CROSS JOIN Table2. Table1 LEFT OUTER JOIN Table2. 1 w NULL NULL Sets of duplicates 1 w NULL NULL. 1 w NULL NULL. 2 x NULL NULL 2 x NULL NULL...
tailieu.vn Xem trực tuyến Tải xuống
In the Unicode model, a single character can be built from several other characters. The code is standard and can be run as-is on other SQL dialects. Implement the standard and depreciate the old syntax
tailieu.vn Xem trực tuyến Tải xuống
92 CHAPTER 5: DATA ENCODING SCHEMES. 5.3 General Guidelines for Designing Encoding Schemes. These are general guidelines for designing encoding schemes in a database, not firm, hard rules. The use of existing standard encoding schemes is always recommended.. Although that sounds obvious, I have worked on a media library database project where the programmers actively avoided talking to the professional...
tailieu.vn Xem trực tuyến Tải xuống
A good heuristic is to order the values in some natural manner, if one exists in the data, so that table lookup will be easier. Another good heuristic is to order the values from most common to least common. That way you will have shorter codes for the most common cases. After arguing for a natural order in the list,...
tailieu.vn Xem trực tuyến Tải xuống
The European Union has rules for computing with euros, and the United States has similar rules for dollars in the Generally Accepted Accounting Practices (GAAP).. it is set for Pascal (Newtons per square meter) and will not tell you how many square meters you have on the surface of the tire or the force exerted by the air, and you...
tailieu.vn Xem trực tuyến Tải xuống
Subjective rating scales (“strongly agree,” “agree. The important principle of measurement theory is that you can convert from one scale to another only if they are of the same type and measure the same attribute. Chinese language and culture have separate words for the same relations based on the genders of your parents’ siblings and the age relationships among them...
tailieu.vn Xem trực tuyến Tải xuống
Database designers do not have infinite storage, so we have to pick a subrange to use in the database when we have no upper or lower bound.. For example, few computer calendar routines will handle geologic time periods, but then few companies have bills that have been outstanding for that long either, so we do not mind.. They both measure...
tailieu.vn Xem trực tuyến Tải xuống
proprietary exposed physical locators will not work in the long run.. “impedance mismatch” in the comp.databases.theory newsgroup in October 2004, one experienced programmer reported:. The data needed consisted of basic information, name of the office location, address, manager, and phone. These object- linking tables are the biggest in the entire database. The values have be recorded in the most general...
tailieu.vn Xem trực tuyến Tải xuống
The actual values of user-controlled keys are determined by users and must therefore be subject to change by them (e.g., if two companies merge, the two employee databases might be combined, with the result that some or all of the serial numbers might be changed).. We did a lot of this in the early days of RDBMS. Attribute splitting consists...
tailieu.vn Xem trực tuyến Tải xuống
3.13 Every Table Must Have a Key to Be a Table 57. A country code at the start of the string determines how to parse the rest of the string, and it can be up to 34 alphanumeric characters in length. This magical, universal, one-size-fits-all numbering is totally nonrelational, depends on the physical state of the hardware at a particular...
tailieu.vn Xem trực tuyến Tải xuống
Example: The open codes in the UPC scheme that a user can assign to his or her own products. The check digit still works the same way, but you have to verify the codes inside your own enterprise.. An exposed physical locator is not based on attributes in the data model and is exposed to the user . The system...
tailieu.vn Xem trực tuyến Tải xuống
If your SQL product has a CREATE DOMAIN statement, you will include DEFAULT and CHECK() constraints in the domain declaration, so the use of the DOMAIN is enough. Multicolumn constraints on columns that are far apart should be moved to the end of the table declaration.. It can also be argued that none of this really matters, because most of...
tailieu.vn Xem trực tuyến Tải xuống
Because NOT NULL is so common, it can be left on the same line as the DEFAULT and data type.. 3.2 The Default Value Should Be the Same Data Type as the Column. Why incur that overhead, when you could get it right in the first place?. 3.3 Do Not Use Proprietary Data Types. Proprietary data types do not port...