Full access to SQL Syntax (2)

SQL syntax for example, the following two examples will have the same effect, and all fields will be returned from the employee table.

For example:

If we want to check out all the records in the employee table, we can do so through the following statement.


SELECT all* from staff form; DISTINCT



　　
The field data that is selected for a table is slightly repetitive, that is, the record results for a field query are unique. For example, there are many staff on the staff form

The data may have the same name, so if we use the Select DISTINCT in the SQL statement, the query results will be filtered for different names. If you put

DISTINCT is omitted, such a query displays all of the records.

Distinctrow

Ignores records that are duplicates of the entire record, rather than just the data for one field.

Table

Specify the tables that are required for the query record.

For example:


SELECT Distinctrow Company Name


From customer form INNER JOIN order Form

On Customer table. Customer id= order form. Customer ID


Order by company name;


If you ignore Distinctrow, the following line of order data is generated for each company. In addition, if the distinctrow is used only in one form, it will be omitted.

Top

Returns data for a specific number of bars, starting with the first or last (using the ORDER BY condition clause).

For example:

When you want to know the name data of the top 25 students in the class in 2000, you can enter a statement like this:

SELECT Top 25 Student Name

form Student Form


WHERE Graduation Year =1994


Order by graduation score average score DESC;


If you do not add the order by this line of conditions, you will get the data, random data. In addition, after the top statement, in addition to adding numbers, you can also use the reserved


Word percent to query.


For example:


SELECT Top percent student name


From student form

Where graduation year =1994


Order by the average DESC graduation results;
　
Use of PARAMETERS (parameter) declarations

For parameter-type query syntax, the operation that declares the name of the parameter and the data type.


PARAMETERS name Datatype[,name datatype[,...]]


Name


The name of the parameters. You can use the parameter name as a string, and if the name contains an empty string, you can use the middle bracket to handle it, for example, "Vbeden".


DataType


Enter the data type of the parameter.


For example:


If you need to enter your name in a mobile query, you can do so by using the following methods:


PARAMETERS "Enter name" Text;


select*

From staff form

WHERE name = "Enter Name:";