In this article, I will tell you about the expressions that form the basis of sql and how to give aliases to columns.
Null values are unknown , unspecified .
When null is entered into an arithmetic operation , the result will be null .
With the SELECT statement , we select the columns to use in the table that we select , or if we use all the columns , we select all the columns in the table by using (*) . As an example of its use :
SELECT kolon_adi FROM tablo_adi or
SELECT * FROM tablo_adi used in the form .
Here I have selected all fields with SELECT * in my SH.CUSTOMERS table .
The From statement specifies our table containing the specified columns .
SELECT * FROM SH.CUSTOMERS;
We use the where statement to restrict the fetch of data, and to bind them to a condition . For example , if we want to see 30-year-old workers in our worker table , we use where .
SELECT*FROM ADMIN.ISCI WHERE yas=30;
Now below is the example that I have made and the result after running the query .
SELECT * FROM SH.CUSTOMERS WHERE CUST_YEAR_OF_BIRTH > 1964;
In this query , we wanted to see those whose birth date is greater than 1964 , and the result of running this query below :
another example :
SELECT * FROM ADMIN.NEW_TABLE WHERE SALARY < 3000;
NAMING OF COLUMNS (ALIAS)
Nicknames given to columns do not cause any changes in our result set , we only use these names in our sql query . Alias are written just after the column name . The AS statement can be written between the column name and the alias we give to the column , but it is not mandatory . AS is used here as “as” . If you want to use as # , $ , , uppercase and lowercase letters and Turkish characters , Alias is written in double quotes .
SELECT CUST_FIRST_NAME "ADI" FROM SH.CUSTOMERS;
Used to merge columns and strings.
Pipe = ‘| | ‘ .
The CONCAT command can be used for merge operations .
SELECT DISTINCT CUST_FIRST_NAME | | ' ' | | CUST_LAST_NAME AS "AD SOYAD" FROM SH.CUSTOMERS;
We use the DISTINCT command to combine multiple but identical lines into a single row . In our example below , we ran this query because we don’t want to see duplicate values in the cust_first_name column .
SELECT DISTINCT CUST_FIRST_NAME FROM SH.CUSTOMERS;
VIEWING TABLE STRUCTURE
The DESCRIBE command is used to display the table structure . Usage :
DESC[RIBE] table_name ;
This is the structure of the sh.costs table you see above .
another example :
See you in my next post.