Microsoft Word - Sam's Teach Yourself MySQL in 21 Days - SAMS.doc
FROM Customer as C, Order as O WHERE C.Customer_ID = O.Customer_ID This is probably the most frequently used of all joins—the pr ...
COUNT() The COUNT() function is used to count the number of occurrences of all non-null values in a column. For example SELECT C ...
This function adds all the values together and returns the sum. STD() The STD() function returns the standard deviation of a giv ...
you would then use the first name to determine in what order the names should come. This is exactly how the ORDER BY clause trea ...
First Name: Jerry Last Name: Maxon Address: 123 N. Hampton Lane Change the name of the last record you added from "Jerry" ...
In the Enterprise, things may be a little different. At the Enterprise level, you may have many client machines accessing your d ...
How Does MySQL Help? MySQL provides a lot of functions that can help perform many tasks. These functions can be used in lieu of ...
It added every row individually. To add the totals of both columns for every row, you would use the following statement: SELECT ...
The MOD() function takes two arguments. The first argument is the numerator, and the second argument is the divisor. To express ...
If the division of Column1 by Column2 was okay—meaning that Column2 did not have a zero value— the result of that division was r ...
LTRIM, RTRIM, TRIM These handy little functions trim excess spaces from either the beginning or the end of a string. These funct ...
LOCATE() The LOCATE() function takes three arguments. The first argument is the string expression you are trying to find. The se ...
Summary MySQL provides a number of internal functions that allow you, the database administrator or application programmer, to a ...
Although threads are similar in principle to processes in UNIX systems, they are not actually the same because the MySQL daemon ...
Figure 11.2 Safer processing with locks. In this simple example, you have used only one table. More commonly, a query will invol ...
If a thread obtains a READ lock, that thread and all other threads can only read from those tables. If a thread obtains a WR ...
Performance An application may need to perform several lines' worth of operations on a number of tables. In this case, the code ...
That's where a key, or index, can help. A key is a field in the table that helps you locate entries in a table in a far more eff ...
You should look at the CREATE TABLE syntax for its full range of syntactical options, because you will concentrate on the ALTER ...
Multiple-Column Keys You can create a multiple-column key, also called a composite index, on more than one column in the same ta ...
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